Official Explanation
Conclusion: "...the Dew Drop Inn will try to bring in new customers during the week of St. Patrick's Day."
Premises: "The Dew Drop Inn... needs to attract new customers in order to survive"; "The bar manager's initial step was to offer drink discounts to the bar's regular patrons if they come to the bar during that week."
Assumption: The Dew Drop Inn's plan to attract new customers will be successful; there are no problems with the plan that will cause it to fail.
You can identify that this argument has a planning pattern because it identifies a problem: the Dew Drop Inn needs to attract new customers in order to survive – and then proposes a solution to that problem: offer discounts to the current regular customers if they come to the bar during the week of St. Patrick's Day. The assumption of any planning argument is that the plan will be successful, and that there are no problems with the plan.
The answer that most strengthens the argument will provide a a reason the plan will be successful, or eliminate a potential problem with the plan.
The answer that most weakens the argument, on the other hand, will point out a problem with the plan – a reason why the plan will not be successful.
The first answer choice is irrelevant; whether the other bars on the street are offering discounted drinks to regular customers does not help determine whether the plan to attract new customers will succeed.
The second answer choice weakens the argument, because it identifies a potential reason the plan might not help to achieve the goal. If potential new customers would object to paying a higher price than the bar's regular patrons, then the plan might not succeed in attracting new customers.
The third answer choice is out of scope. Whether many of the bars on the same street plan to advertise heavily in advance of St. Patrick's Day does not help determine whether the Dew Drop Inn's plan will be successful.
The fourth answer choice strengthens the argument, because it provides a reason why the plan may actually succeed: if a bar that already has a number of patrons in it is likely to draw additional patrons, while revelers will often pass up a bar that is largely empty, then the plan to ensure regulars are present might help the plan succeed.
The fifth answer choice is irrelevant; the fact that most of the Dew Drop Inn's regular customers are also regulars at the other bars on the same street does not determine whether the Dew Drop Inn's plan will work.
The sixth answer choice is out of scope; if the Dew Drop Inn offers fewer imported beers on tap than it did when it was more successful, there is no way to know whether this would help or hinder the plan's success.
Answer:
Strengthen: A bar that already has a number of patrons in it is likely to draw additional patrons, while revelers will often pass up a bar that is largely empty.
Weaken: Potential new customers would object to paying higher prices than the bar's regular patrons.