how much would adam have to deposit in a savings account to earn 100$ in interest over 4 years at a 5% simple annual interest rate?

Interest I   =   PRT/100    for Simple Interest Where P = Principal,             R = Rate  in percentage per year             T = Time  in years. 100 =    P * 5 * 4 /100 100  =    20P /100 100 * 100 = 20P P =    100 * 100 / 20 P = 500. Principal  = $ 500. Adam would have to deposit  $500.