An open box can hold 80 cm3. It is made from a square piece of tinplate with 3 cm squares cut from each of its 4 corners. Find the dimensions of the original piece of tinplate.

Let the side of the square plate be x cm.

The height of the box is 3 cm.

The length & width are both (x-6) cm.

volume = length*width*height

=3 * (x-6) * (x-6)

=80

x can then be obtained by solving

3 (x-6) (x-6) = 80