Let the length of one side of the original square be a.
The length of one side of the new square is (a+7) feet,
the area of the second square is [tex] (a+7)^{2}=121 [/tex]
taking the square root of both sides:
[tex] \sqrt{(a+7)^{2}} = \sqrt{121} [/tex]
a+7=11
a=4
Answer: 4 feet
