A builder wishes to fence in 80000m280000m2 of land in a rectangular shape. For security reasons, the fence along the front part of the land will cost $60 per meter, while the fence for the other three sides will cost $20 permeter.

How much of each type of fence should the builder buy to minimize the cost of thefence?

Determine the length of the fence along the front part of the land that will be cost $60 per meter.