the blue is the hint for help

the black is the question

7 years ago, you started donating $351 to a charity organization every year. You plan to continue to donate in the next 6 year(s). The discount rate is 6.7%. Please find the present value of your donations. [Hints/Example) Hint: First find the present value of the annuity at the time point of 7+1 years ago. Please count the periods carefully. Example: 7 years ago, you started donating $406 to a charity organization every year. You plan to continue to donate in the next 8 year(s). The discount rate is 5.6%. Please find the present value of your donations. Sclution: There are many ways to solve the problem. The following is only one of them. Eight years ago, the value of a perpetuity that starts 7 years ago is V. 8=$406/5.6%=$7250. Eight years from now, the value of a perpetuity that starts in 9 years is V8-$406/5.6%=$7250. Its value 8 years agao is Vg/(1+r)16=$7250/(1+5.6%)16=$3031.9031. The difference between the the values of the two perpetuities 8 years ago is $7250 - $3031.9031 = $4218.0969 (notice that it is exact what the simple formula predicts: $406/5.6% - $406/(1+5.6%)16=$4218.0969). The present value of the $4218.0969 is $4218.0969*1.05648=$6522.71.