After graduating from Parktown High School, Peter works for four years. During this time he deposits each month R1,000 on a savings account at an annual interest rate of 5% (no initial deposit). The next four years Peter spends at WITS. During this time, he withdraws each month an amount of Rp from his savings account so that at the end of the four years the account balance is zero again. The total interest earned on Peter's saving account is