Yolanda borrows P at an annual effective rate if 5%. She agrees to repay the loan by making the following payments: A payment of 500 at the end of year 2, a payment of 450 at the end of year 4, a payment of 600 at the end of year 5, and and a payment of X at the end of year 7. The method of equated time can be used to determine that Yolanda could have also repaid the loan by making a payment of 1550+X at approximately time t = 4.1944. Find X.