Harriet wishes to accumulate $60,000 in a fund at the end of 25 years. She plans to deposit $80 into the fund at the end of each of the first 120 months. She then plans to deposit $80 + x into the fund at the end of each of the last 180 months. Assume the fund earns interest at an annual effective rate of 3.66%. Determine x.

Please show all working clearly.