#### Answer

5 inches

#### Work Step by Step

x is the length and width of the open box
The volume of box is represented by the following equation:
$x\times x\times3=75$
Simplify.
$3x^2=75$
Divide each side by 3.
$3x^2\div 3=75\div3$
Simplify.
$x^2=25$
Take the square root of each side.
$\sqrt{x^2}=\sqrt{25}$
Simplify.
$x=5$