~Hello There!~
Since there are equal amounts of each color, there are 2 pints of blue and 2 pints of yellow. In order to be 80% yellow, the new color needs to be 20% blue.
2/0.2 = 10
To make 10 pints, 6 pints of yellow should be added to the bucket.
Therefore, Brandon is correct as you would need to add 6 pints of yellow in order to make it 80% yellow.
Hope This Helps You!
Good Luck :)
Have A Great Day ^_^
- Hannah ❤