A farmer wants to enclose an area of 1500 square metres. Suppose that along the road adjoining his property he would like to use a more expensive fence, and that no fence is needed along one side of the area perpendicular to the road as it is bounded by a river.

Ive made an image to represent this below. Excuse my crude use of paint!.....

my questions are... explain why Y = 1500/X? ,

and how do I show that the quantity to be minimised is

C = 40X + 22500/X ?