Question

3. If i gallon of paint covers of the wall,

Answer 1

-- To finish painting the entire wall, you have to paint 1/3 of it 3 times.

-- Each time you paint 1/3 of it, you need 3/4 of a gallon of paint.

-- (3/4 gallon) x (3 times) = 9/4 gallon = 2-1/4 gallons, if you don't spill any.