Help I keep getting an answer that is not an option

Answer:
6600
Step-by-step explanation:
y = 15000( 1.2) ^ (x/3)
Let x = 6 years
y = 15000( 1.2) ^ (6/3)
y = 15000( 1.2) ^ (2)
y = 15000( 1.44)
y =21600
This is the total amount in the account
We want the profit
Subtract the original amount in the account
21600-15000
6600