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