Principal Amount (P) = $10,000
Interest Rate (I) = 7.5% (0.075)
Time Period (N) = 20 years
Future Value (FV) = Principal(P) * (1+Interest (I))^(N)
10,000*(1+0.075)^20 = $ 42,478.51 (this is what your initial investment will grow into at the end of 20 years)