Final answer:
To find the maximum number of visits to the art museum for a total cost of 15 visits, divide the remaining cost ($15) by the cost per visit ($2). The maximum number of visits is 7 visits.
Step-by-step explanation:
To find the maximum number of visits to the art museum for a total cost of 15 visits, we need to calculate how many visits can be made after paying $21 for the membership. With the membership, each visit costs $2. So, after paying $21, the remaining cost for visits is $15 (total cost of 15 visits - $21 membership fee).
Since each visit costs $2, we can divide the remaining cost by the cost per visit to find the maximum number of visits. $15 / $2 = 7.5 visits. However, since we cannot have a fraction of a visit, the maximum number of visits is 7 visits.