Question 1991
classic question...

draw a diagram of a square, side x. In each corner draw a little square (the bit that will be cut out). Call its side length, y.

Once the sides are folded up to form the container, it will have a volume given by its base area*height

volume, V = (x-2y)(x-2y)(y)

so {{{V = 128 = x^2y - 4xy^2 + 4y^3}}}

You have 2 things you do not know but one equation...you cannot solve this.

You have to be given some other piece of information. Have a look at the question and see if you have missed anything out. Such as the size of y or the area of the original plate.

jon