The problem is discrete, because the cost of movies cannot be below zero, and neither can the number of movies purchased
The expression for the balance (b) in terms of the number of years (t) can be written as
... b = 2000·2^(t/19) . . . . . . the amount grows exponentially, and is is doubled when t=19
Then for t=5, the balance is
... b = 2000·2^(5/19) ≈ 2400
The best choice is ...
... A. $2400
