Answer
7 feet
Work Step by Step
Let x be the length of a side of the original square. If the area of the new square is 169 square meters then:
$169=(x+3+3)^2$
Simplify.
$169=(x+6)^2$
Take the square root of each side.
$\sqrt{169}=\sqrt{(x+6)^2}$
Simplify.
$13=x+6$
Subtract 6 from each side.
$13-6=x+6-6$
Simplify.
$7=x$
