A twenty-year loan of $25000 is negotiated with the borrower agreeing to repay principal and interest at 5%. A level payment of $1500 will apply during the first ten years, and a higher level payment will apply over the remaining ten years. Each time the lender receives a payment from the borrower, he will deposit the portion representing principal into a sinking fund with an annual effective interest rate of 4%. (This is the amount for replacement capital). What is the lender's yield rate on this entire investment?

Answer is 4.78740%. Please solve this.