First take note he only has $20 and the bag he must buy is $12.55. Also the loose seeds are $1.49 per pound.
To solve subtract 12.55 from 20
20-12.55=7.45
So after buying the 10 lb bag he has $7.45 left now divide that by 1.49
7.45/1.49=5
So after buying the 10 lb bag he can also buy 5 lb of the loose seeds!