The problem wants to find out the cash flow per period that Robert will make from his 40th birthday until his 65th birthday. We know that he wants to get $500,000 by his 65th birthday thus this is the future value of his money. To solve for the cash flow per period, the equation is Future value = Annuity * [((1+i)^n-1)/i]. The n is the number of payments Robert would make which is 25. The answer would be $3749.98.