If $6200 is invested in a savings account for which interest is compounded semiannually, and if the $6200 turns into $7100 in 3 years, what is the interest rate of the savings account? A.14.02% B. 3.42% C. 6.89% D.4.57%

The account balance A in terms of the principal P invested is
  A = P*(1 +r/n)^(nt)
  7100 = 6200*(1 +r/2)^(2*3)
  (7100/6200)^(1/6) = 1 +r/2
  2*(71/62)^(1/6) -1) = r ≈ 4.57% . . . . . . . . matches selection D