Answer: He would have spent 10 dollars on snacks.
Step-by-step explanation: If Brock buys $9 on healthy food, he will then buy $1 of snacks. This creates an addition problem of 9+1=10. If you were to take that problem and multiply it by ten you would get 90+10=100. So with Brock spending $90 on healthy food, he has spent another $10 on snacks.