#### Answer

x = 320

#### Work Step by Step

0.10x + 0.12(720 - x) = 80
Multiply both sides by 100 to free the equation of all decimals, and then use the distributive property.
10x + 12(720 - x) = 8000
10x + 8640 - 12x = 8000
In order to solve for x, we first need to get all of the terms with an x in them on the same side of the equation.
10x - 12x = 8000 - 8640
-2x = -640
Divide both sides by -2.
x = 320