This is already written with positive exponent
3 · t - 12 = 40
3t - 12 = 40 |add 12 to both sides
3t = 52 |divide both sides by 3
t = 52/3
t = 17 1/3
The formula required to answer this is:

where A is the amount of the principal P after n compounding periods per year at r interest rate (as a decimal fraction).
Plugging in the given values, we get:

Rounding to the nearest dollar, we get $662.00. Therefore a is the best answer choice.