If half a gallon of paint covers 1/6 of a wall, then we need 6 1/2 gallons of paint. To make this simpler, we can just say that a gallon of paint can cover 2/6 of the wall. This means that with 2 gallons of paint, we can cover 4/6 of the wall. 3 gallons of paint will cover 6/6 of the wall.
–5 × 0.75 × 20 could be rewritten (applying the associative property) as –5 × (0.75 × 20). I chose this configuration because 0.75 * 20 is 15. Next, evaluate -5(15). This is -75. This matches Answer D.