17. the amount a of money in an account after simple interest has been earned is given by the formula a = p + prt where p is the principal, r is the annual interest rate in decimal form, and t is the time in years. a. solve the formula for r b. the amount of money in an account after interest has been earned is $1080, the principal is $1000, and the time is 2 years. what is the annual interest rate? c. solve the formula for p. pl