Answer:
1.5 gallons
Step-by-step explanation:
Since the ratio 3:7 would make 10 gallons of green paint, you must find how much blue paint is needed. If you divide 7 by 2, you get 3.5, and 5 minus 3.5 is 1.5. So the answer is 1.5 gallons because if the total amount is 5 gallons, and 1.5 plus 3.5 is 5, this is the answer.