Final answer:
The explicit expression that represents the number of seats in a row is (a(n) = 15 + (n - 1)3).
Step-by-step explanation:
The correct explicit expression that represents the number of seats in a row is option A: (a(n) = 15 + (n - 1)3).
This expression starts with 15 as the first row, and then adds 3 additional seats for each subsequent row. The term (n - 1)3 accounts for the extra seats added for each row after the first row.
For example, if we substitute n = 5 into the expression, we would get: a(5) = 15 + (5 - 1)3 = 15 + 4 * 3 = 15 + 12 = 27. So the fifth row would have 27 seats.