Barney wants to start saving for his retirement. Starting today, he will make monthly deposits to his RRSP for 20 years. One month after his last deposit, he wants to withdraw $4,000 per month for 10 years. Assume the invested funds earn 6% compounded monthly for the entire time. a) How much must Barney deposit into his RRSP per month to achieve his goal? b) How much interest will Barney earn over the 30 years?