18. if the volume of a cube is 8cm, the cube root of that is 2 cm (because 2 x 2 x 2 = 8), so each side of the square of each side of the cube is 2cm. Its surface area is 2x2 (area of each side) x 6 because the cube has 6 sides, so 2 x 2 x 6 = 24 square cm.
17. The chance of getting an even number is 3/6 or 1/2, and the chance of flipping a tail is 1/2. So out of all 12 possibilities (because 6 x 2 is 12), 3 of those would involve both an even number and a tail.