12,000 is compounded semiannually at a rate of % for 20 yrs

APR = 6%?.

P = Po(1+r)^n.

Po = 12,000 = Initial investment.

r = 0.06/2 = 0.03 = Semi-annual % rate expressed as a decimal.

n = 2comp./yr. * 20yrs. = 40 Compounding periods.