An S&L pays 5% per annum compounded quarterly. Bert and Bertha are now 50 years old. They will deposit $200 per quarter at the end of each quarter until they are 65 years old. How much is in their retirement account at the end of this period i.e. at 65? 3 months after their last deposit they start withdrawing equal amounts each quarter until they are 80 i.e. for the next 15 years Find the size of the withdrawals. How much cash did they deposit? How much cash did they withdraw? What was the total interest?

(I need a step-by-step explanation of the formulas used. Thanks)