High School

Suppose you need to minimize the cost of fencing in a rectangular region with a total area of 450 square feet. The material for three sides costs $21 per linear foot, and the material for the fourth side costs $15 per linear foot.

Write a function that expresses the cost of fencing the region in terms of the length, [tex]x[/tex], of the two opposite sides of the region with material costs of $21 per linear foot.