Alexis needs to paint the four exterior walls of a large rectangular barn. The length of the barn is 80 feet, the width is 50 feet, and the height is 30 feet. The paint costs $28 per gallon, and each gallon covers 420 square feet. How much will it cost Alexis to paint the barn? Explain your work.

First we need to find the area of the barn's walls.

2 (length x height) + 2 (width x height)

=2 (80x30) + 2 (50x30)

=2 (2400) + 2 (1500)

=4800+3000

=7800 ft^2

Now we can find the amount of gallons needed, then the total cost.

7800 ft^2/420 ft^2

=18.57 gallons

=19 gallons

19 gallons x $28

=$532

It will cost $532 to paint the barn