$15,000 was invested, from which can be withdrawn a geometric gradient series of annual payments decreasing at...

Question:

$15,000 was invested, from which can be withdrawn a geometric gradient series of annual payments decreasing at the rate of 10% per year. The first payment received was $3,000 and it occurred after the investment followed by the remaining five payments (total of six withdrawals). What is the rate of interest earned on this investment?