Soda concentrate is being added into a soda-making machine in a manufa

We'll first break our question stem into small bits so it is easier to turn into equations and understand.
This is a Precise approach.

concentrate = added at constant rate, let's call this c
prepared soda = removed at constant rate, let's call this s
so in total volume change is c - s

We need to find s.

(1) this doesn't tell us anything about the rates.
Insufficient.

(2) so c = 25 and total volume change is 75, that is c - s = -75. Substituting c = 25 gives s = 100.
Sufficient!

(B) is our answer.

**note that this answer assumes that the only thing pumped out of the machine is prepared soda and the only thing pumped in is concentrate. This is usually made explicit in the question but, if it isn't, is a reasonable assumption. If you find yourself inventing new data - you're doing something wrong!
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1. Considering the first option we can't decide anything about the rate of outflow of soda from the machine. We have no idea in how much time the machine is becoming empty. If the time to become empty were there, then we could have calculated the outflow rate. Not Sufficient.

2. Here we have been given both inflow and resulting volume of the machine. From this, we can calculate the outflow rate assuming there is no other addition or subtraction.
It is sufficient to answer.

So answer is B.