I am working on a business calculus problem and I need help understanding the step on how to solve this problem. I have included the question along with the answer in the image I provided. Thank you.

?

An owner wishes to enclose a garden with an area of 1.80!) square feet. As before, three sides of the fence will be constructed with chicken wire at a cost of 52 per linear foot. and the fourth side will be constructed with cedar fencing at a cost of $6 per linear foot. what is the minimum cost of building a fence that will enclose a garden with an area of 1,300 square feet? What are the dimensions of this garden? Answer The dimensions that minimize the cost of a 1.5m square foot garden are an feet by ED feet. and the minimum cost is 543D