The length (L) is 4 more than the width (W) means L = 4 + W

Now, the sides are modified.

The length becomes L -2 and the new width is W + 2 and it is a square.

The area of the square = 324, so the equal sides must be 18 and 18.

The original length is 20.

The original width is 16.

Note that L=16 and W=20 is not correct. Explain why.