Larry Smart has $10,000 which he can invest today. in addition to this amount, he can also invest $2,500 per year for thirty years (beginning one year from now) at which time he will retire. he plans on living for twenty years after he retires. if interest rates are 5%, what size annual annuity payment can he obtain for his retirement years?

The answer is 16,796 but I don't know how this answer was achieved.