Final answer:
The expression for the surface area of the cube is A = 6x².
Step-by-step explanation:
The surface area of a cube is given by the formula A = 6s², where s represents the length of each side of the cube. So, to find the expression for the surface area, A, of a cube with side x, we substitute x for s in the formula. Therefore, the expression for the surface area of the cube is A = 6x², which corresponds to option A.