It takes three 1-gallon buckets to paint 72sqft, if you simplify or find the unit rate, you can know that you can paint 24sqft with one 1-gallon bucket of paint. Since you need to paint 90 sqft, you can’t use three buckets because it only covers 72sqft, but if you use 4 buckets, it will cover 96sqft.
THE ANSWER IS 4 1-GALLON BUCKETS OF PAINT