Answer:
1050
Explanation:
So, we know 4/5 of a gallon can paint 280ft^2, but we don't know how much each gallon can paint, so to find x, do this
4/5x=280ft^2, next multiply both sides by 5/4 to get x by itself
x=350
Now multiply x by 3 to get your new answer.
350*3=1050
Hope this helps, feel free to leave any questions.