### Home > CAAC > Chapter 16 > Lesson 16.9.1.3 > Problem 9-39

9-39.

Write and expression for the area and multiply that by the cost per square foot.

Area: *x*^{2}

Cost: 3*x*^{2}

Write an expression for the area of one side.

Write an expression for the area of four sides.

Write an expression for the cost of four sides.

Area: 4*xh*

Cost: (1)(4*xh*) = 4*xh*

This is the sum of your expressions from parts (a) and (b).

100 = *x*^{2}*h*

Substitute '*h*' into the equation in part (c).