Answer
$5$ inches.
Work Step by Step
Let the length of the side of the square be $L$.
Increased length = $L+3$.
$A=(length)^2$.
Thus:
$A=(L+3)^2$
From the question we have $A=64$ square inches.
$64=(L+3)^2$
$8^2=(L+3)^2$
Take the square root of both sides.
$\pm \sqrt{8^2}=\sqrt{(L+3)^2}$
Simplify.
$\pm 8=L+3$
This gives:
$+ 8=L+3$
Subtract $3$ from both sides.
$+ 8-3=L+3-3$
Simplify.
$5=L$.
