To answer the problem above, I assume that the interest is compounded. Having said that, the equation for the future worth (F) of the present investment (P) is,
F = P x (1 + i)^n
where i is interest rate and n is the number of years. Substituting,
F = ($15,000) x (1 + 0.07)^3 = $18,375.645
Thus, the answer to the question is approximately $18,375.65.