If the correct answer is what you say, there is a crucial piece of information missing from the problem statement. How often is the interest compounded?

For compound interest, a one-time investment of a principal amount P at an annual interest rate I compounded n times per year for m years will have a maturity value of A.

A = P(1+ (I/n))^(n*m)

Putting your numbers into this equation and assuming quarterly compounding, we get

A = 1400(1 + (.16/4))^(4*6)

This is easily evaluated by the Google search box to give

1 400 * ((1 + (.16 / 4))^(4 * 6)) = 3 588.62583

So we conclude

For compound interest, a one-time investment of a principal amount P at an annual interest rate I compounded n times per year for m years will have a maturity value of A.

A = P(1+ (I/n))^(n*m)

Putting your numbers into this equation and assuming quarterly compounding, we get

A = 1400(1 + (.16/4))^(4*6)

This is easily evaluated by the Google search box to give

1 400 * ((1 + (.16 / 4))^(4 * 6)) = 3 588.62583

So we conclude

**A = 3,588.63**