Aiming for a needed area

You re told that llamas need a certain amount of grazing area in order to thrive. Armed with the area constraints, you can go about figuring out how to create the needed room for a hungry llama. 

The Problem You need to create a rectangular area encompassing 6,400 square feet, in which the length is 40 feet less than three times the width. One side of the rectangular area will be along a river, so you don t need to put a fence there. What is the least amount of fencing needed to partition off that rectangular area  

Part IV Taking the Shape of Geometric Word Problems 

Iu Have the length of the area be along the river. v Let the width be along the river. 

In both cases, the area is length times width or (3w - 40 )w. So solve the equation A = Iw, replacing the A with 6,400. 

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