An investment pays $20,000 at the end of year 2, $30,000 at the end of year 4 and $X at the end of year 8. At an annual effective rate of 8.5%, the modified duration of this cash flow is 5.51704. Calculate X (round your answer to integer).

Show all works, and please show ur work it with math steps and illustrations instead of excel tables!! Thank you! I will thumb up if it's correct!