Answer
$5$ inches
Work Step by Step
Put the given information into formulas. Use them to solve for $s$. $S^2$ is the equivalent of $s+3$ here. Find the square root of both sides and then isolate $s$ to get its values. Only the positive value matters since we are dealing with a shape.
$S=s+3$
$S^2=64$
$(s+3)^2=64$
$s+3=±8$
$s=-11,5$
$s=5$
