The city of Workney, in raising bus fares from $1.00 to $1.25, propose

As with all GMAT CR questions, it's best to stick to a simple, flexible process rather than trying to pigeonhole questions into "types" and switching up your process on each question (more on our recommended process here).

First, let's break down the structure of the passage.

We first hear about an issue, and the city of Workney's proposed solution to the issue:

• The passage opens with a fact: The city of Workney is "raising bus fares from $1.00 to $1.25."
• There is an issue with this fact: the increased bus fare will create an "extra burden... on the city’s poor people"
• The city comes up with a plan to solve the above issue: they'll offer a discount when you buy a bunch of tickets at once! Specifically, "18 fare tokens [will] be sold for $20.00."

However, some people are critical of the above plan.

• These critics have offered an alternative plan: "that 9 fare tokens be sold for $10.00." Notice that this results in the same price per ticket as the "18 for $20" plan -- under each plan, people will have to pay about $1.11 per ticket.
• So, how do the critics support their alternate plan? They say that "a $20.00 outlay would be prohibitive for poor riders." In other words, poor people will struggle to come up with the $20, so they need an option that doesn't cost so much up front.

The question asks which answer choice is an assumption on which the alternative proposal depends. So, we're looking for something that MUST be true in order for the "alternative plan" to make any sense.
Critics have proposed their alternative plan to address a specific issue: that $20 is too much for poor bus riders to pay at once. Does this plan depend on poor residents riding the bus just as much as they used to?

Not necessarily. Maybe some poor residents will choose to walk instead of ride the bus when the fares increase, even if they CAN afford to pay for the "9 for $10" plan. As long as the critics' plan resolves the issue of the $20 upfront charge, it doesn't matter if the number of poor residents riding the bus remains exactly the same after the fare increase.

Eliminate (A).

Again, the point of the alternate plan is to make it so poor people don't have to pay $20 at one time. It doesn't matter if riders who are NOT poor also take advantage of the deal.

(B) doesn't HAVE to be true, so get rid of it.

This one HAS to be true for the critics' plan to make any sense. The argument against the "18 for $20" plan is that $20 is too much for poor people to pay all at once. So, what if that's true of the "9 for $10" plan as well? Then the alternative plan doesn't fix the problem at all.

The alternative plan depends on (C), so (C) is the correct answer.

The purpose of the alternate plan is to lessen the burden of increased bus fares on poor people. It doesn't matter why the fares are being raised in the first place -- perhaps the city is purchasing new buses, or perhaps the mayor will use the funds to install golden toilets in her mansion. The use of the fares doesn't change the fact that $20 is too much for a poor bus rider to pay at one time.

The argument doesn't depend on the fares being used for new buses, so (D) is out.

The critics argue that the "9 for $10" deal is best because poor people are UNABLE to pay $20 all at once. So, does it need to be true that people in general will more regularly purchase the "9 for $10" deal?

Not necessarily. Maybe the richer people in town would actually prefer the "18 for $20" deal for some reason, and would purchase this package more regularly. Maybe the opposite is true, and rich people as well as poor people prefer the "9 for $10" deal.

So, it's not 100% necessary that people WOULD buy the "9 for $10" deal more regularly. It just matters that poor people are ABLE to pay the $10 upfront.

For this reason, you can get rid of (E).

(C) is the correct answer.

I hope that helps!