The volume of a rectangular prism is W*H*L
W=Width
L=Length
H+Height
We know that 16=W*H*L
We know the Length and the height are equal because they are both 2 meters less than the width, so lets rewrite this and add an equation
16=W*H^2 (this is height squared because we changed Length to Height since they are equal)
And add the equation
W-2=H
Lets plug in this Height value into our equation
16=W*(W-2)^2
16=W*(W^2-4W+4)
16=W^3-4W^2+4W
W^3-4W^2+4W-16=0
Im not sure how it expects you to solve this without a graphing calculator, maybe someone can clarify this, but the only possible root at this point is W=4
With this we know L and H=2
So the dimensions are
4x2x2