x for the width. 4x for the length. Your equation would be (4x+x)2=100. Simplify like terms, you get 2(5x)=100. Then distribute and you get 10x=100. Divide each side by 10 and you get x=10. 10 is your width. If your length is 4 times the width, you multiply 10 by 4. Your length is 40. Multiply 40 by 10 and you get 400. 400 is your answer.