If 3/4 of a gallon of paint covers 2/5 of a wall, then how many gallons are needed to paint the entire wall?
2 gallons of paint
If 3/4 of a gallon covers 2/5 of a wall, this means that a half of 3/4 gallons can cover 1/5 of a wall.
By knowing this, you can just make up your own expression
(the trick is to find a way to break it down to one, so you can multiply and manipulate it to save yourself some brain cells)
since we're talking about real life it would be 2 gallons of paint instead of 1.875 gallons to paint the whole wall