Keep in mind that the dimensions of the cube are identical in 6 directions. This means that the surface area of the bottom is 5 cm by 5 cm, yielding the area 25 cm^2. The top has the same area, so considering top and bottom we get a total surface area of 50 cm^2.
Likewise, the total surface area of the sides together is 50 cm^2. The total surface area of the front and back together is 50 cm^2.
Thus, the total surface area of the entirre cube is 3(50 cm^2), or 150 cm^2
