Using compound interest formula, what principal does Andrew need to invest at 15% compounding annually so that he ends up with $10,000 at the end of five years? Using compound interest formula, what annual interest rate would cause an investment of $5,000 to increase to $7,000 in 5 years? Using compound interest formula, how long would it take for an investment of $15,000 to increase to $45,000 if the annual compound interest rate is 2%?