Answer:
7
Explanation:
We know that the first store charges $12.50 per month, which is a initial condition, and charges additionally $1.50 per movie, which is variable, this represents the ratio of change, so this can be expressed as

Where
represents movies.
Now, the second store doesn't charge and membership fee, just it charges a cost per movie which is $3.50.
Then, to solve the minimum number of movies needed to Plan A be the best choice, we just have to solve the following inequality

Which expresses the case where Plan A is a better choice, solving for
, we have

Which means that the minimum number of movies is 7, which is the next whole number after 6.