Your problem quite confusing:
10.39% per month is over 120% per year!
Stated is Lenny gets degree in 22 years; then in 32 months?
Anyway, if question is SIMPLY: how much did the parents deposit?
then an interest rate is not necessary.
Looks to me that answer is:
Total deposited = (a+0b) + (a+1b) + (a+2b) + (a+3b) +.....+ (a+30b) + (a+31b).