It's compounded monthly, so 9%/12 + 1 = 1.0075
He puts in $100 every year at the beginning and so, by the time next year comes, it would have been compounded 12 times.
Therefore:
A1 = 100 (1.0075)^12*20
= 100 (1.0075)*240
A2 = 100 (1.0075)*228
A3 = 100 (1.0075)*216
...
...
A19 = 100...