First we need to calculate the are of each wall, since we alredy knew the length (l) and the width (w) which is the height of the wall in this case:
A = wl = 9 . 12 = 108 (ft²)
We also know that he painted 3 walls, we need to multiply our first result by 3, in other words, the area of wall that Brett painted is the sum of the area of three walls: 108 . 3 = 324 (ft²)
Decimals are great for when you are dealing with money and want to round up, and fractions are used when baking (such as need 1/4 or a half cup of something)
The formula for graphing is y=mx+b, where m is the slope and b is the slope-intercept (where the line is at x=0). In this case, the slope is 10. Hope this helps and please give branliest!