这道题目在ASM FM第174页，题干是
Harrier 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 plan 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.

参考答案是

800*s(300|j)+x*s(180|j)=60,000  j=1.0366^(1/12)
得出x=88.86
这个方法我也懂

但是我用计算器算
先算前120个月的av
0.3【I/Y】120【N】80【+|-】【PMT】【CPT】【FV】
得到的结果是11,534.8578

然后算后180个月
【2ND】【FV】0.3【I|Y】11,534.8578【PV】180【N】60,000【FV】【CPT】【PMT】
之后的结果为什么是-334,9103？
根据标准答案，不应该是-（x+80）=-168.86吗