Let the length of the rectangle be x, then the width of the rectangle is 150/x, and the total cost of the fence material is Y. When the short side is taken as the front, the column of the title is y = 6 * 3x+3 * 3 (xa+b ≧ 2 *150/x) = 27x+27.

The minimum cost is: y=540 yuan when the short side is positive, and y=550 yuan when the long side is positive. I hope you can be satisfied!