Watermelons cost $0.35 per pound. joseph’s watermelon costs between $4.20 and $5.25. which compound inequality correctly represents the possible weights of his watermelon?

The answer is 12 < x < 15

x - the weight of Joseph's watermelon 

Watermelons cost $0.35 per pound:
0.35x

Joseph’s watermelon costs between $4.20 and $5.25:
4.20 < 0.35x < 5.25

Divide all by 0.35:
4.20/0.35 < 0.35x/0.35 < 5.25/0.35
12 < x < 15