Final answer:
The expression for the volume, V(x), in cubic millimeters of an open-top box with side length x, when the cardboard is 10mm by 10mm, is V(x) = 10^2h, where h is the height of the box.
Step-by-step explanation:
The volume, V(x), of an open-top box with side length x is given by the formula V(x) = x^2h, where x is the side length and h is the height of the box. In this case, the cardboard is 10mm by 10mm, so the side length x is 10mm.
The height is not given in the question, so it cannot be determined. Therefore, the expression for the volume, V(x), in cubic millimeters of the box is V(x) = 10^2h.