(28÷4)+3+(10-8)x 5 please try to help asap

Which of the following is not a subset of {1,2,3}?

Fatima plans to spend at least $15 and at most $20 dollars on sketch pads and pencils. if she buys 2 sketchpads, how many pemcils can she buy while staying in her price range? fatima can buy between and pencils. ? (type whole numbers. use ascending? order.)

Could someone me with this question i’ve been stuck on it for 20 minutes