Answer: 12 blue, 8 Yellow
Explanation:
If you know there are 5 total parts in paint b, divide the total gallons by parts to find how many gallons is a part. 20 divided by 5 is 4 so 4 gallons in a part.
Then multiply by the parts for each color so 4 x 3 and 4 x 2 to get 12 blue and 8 yellow