The formula for the future value V (in dollars) of an investment earning simple interest is V=p+prt, where p (in dollars) is the principal, r is the annual interest rate (in decimal form) and t is the time (in years). a. Solve the formula for p .

p=

b. An investment earns 9% simple interest. What amount of principal is needed to have $4000 after 3 years? Round your answer to the nearest cent.

Amount of principal: $