Algebra 1 homework help? I've been working on this for over 20 min!!?

Ok, you know that the ending area is 144 m2 and that it is a square. That means all sides are equal in length. The square root of 144 is 12, so the end length of each side is 12 (after 7m was added). So by subtracting (12 - 7), we are left with 5m which was the original length for each side.