Question

Monique had $20. She spent $5 on lunch and $10 at the bookstore.

Answer 1

It's 20-15 Which equals to $5
Add 10+5 together to get 15 then subtract it from 20
Or subtract 5 from 20 to get 15, and subtract 10 from 15 to get 5.
Whichever is easier

Answer 2

20-5=15
15-10=5
She has $5 left