the parameter of a rectangular placemat is 72 in. the length is 4 in. find the with and the length
You must mean perimeter. Parameter has a different mathematical meaning.
Call the length and width L and W.
You already said that the length is 4, but I think you left some words out. Why would they tell you the length and then ask you what it is? A 4 inch length would require the width to be much longer, which makes no sense either.
Didn't they really say that the length is 4 inches LONGER THAN THE WIDTH? If so, then
L + W = 36
L - W = 4
2L = 40
L = 20
W = 16
You need to be more careful spelling and typing in your questions