Width = 6
Length = 30
We know the perimeter of a rectangle is simply twice the sum of it's length and width. So we have the expression:
72 = 2*(L + W)
And since we also know for this rectangle that it's length is 6 more than 4 times it's width, we have this equation as well:
L = 6 + 4*W
So let's determine what the dimensions are. Since we have a nice equation that expresses length in terms of width, let's substitute that equation into the equation we have for the perimeter and solve. So:
72 = 2*(L + W)
72 = 2*(6 + 4*W + W)
72 = 2*(6 + 5*W)
72 = 12 + 10*W
60 = 10*W
6 = W
So we now know that the width is 6. And since we have an expression telling us the length when given the width, we can easily determine the length. So:
L = 6 + 4*W
L = 6 + 4*6
L = 6 + 24
L = 30
And now we know the length as well.
