Objective and Constraint: fencing field alongside river

[so_confused]

I am confused on how to find the equations of the objectives and the constraint, can somebody help me.

A farmer wishes to enclose a rectangular pasture next to a river. To provide enough grass for the herd, the pasture must contain 90,000 square meters of area. No fencing is required along the river. If the farmer wants to minimize the amount of fencing required, what are his objective (the quantity to minimize) and the constraint (the condition the variables must obey) equations?

 

[galactus]

First, identify what is given: the area. How would you express area?.

How about the amount of fence?. What is an equation for perimeter of the fenced area?. Remember, none along the river. You could start by letting the length equal L and the width equal W.