Question

an open rectagular box with length of 6 feet, width of 4 feet and height of 2.5 feet is to be painted on all exterior sides, including the bottom,
with a special waterproof coating. Each gallon of this special coating covers 12 square feet of surface area and costs $36.00. The box
is then to be filled with water that weighs approximately 62 pounds per cubic foot.

Answer 1

If I were filling it with water, I would use the waterproof paint on the inside I think :)

area of bottom = 4*6 = 24 ft^2

area of ends = 2 * 4 * 2.5 =20 ft^2

area of sides = 2 * 6 * 2.5 = 30 ft^2

total area of exterior (no top on it) = 74 ft^2

cost of paint = (36/12)*74 = $222 if you can buy a part of a gallon but if the store only sells whole gallons then we need
74/12 = 6.16 gallons
so we must buy 7 gallons
cost = 7 * 36 = $252
and we use the rest of the can to paint the roof of our truck.

the volume of the box is 6*4*2.5 = 60 ft^2 which at 62 pounds per gallon (fresh water, don't see much of that, ours weighs 64) = 3,720 pounds of ater