the cost of painting a wall varies directly with the area of the wall. Write a formula for the cost of painting a rectangular wall with dimensions l by w. With respect to l and w, does the cost vay directly, jointly, or inversely?

The area of the wall is l*w, which the cost is directly related to.

Therefore, the formula is c = l*w.

The cost is jointly varied, because the cost is related to the length and the width, multiplied. (The jointly variation equation is y = kxz, which the formula we made is similar to)