With vectors a = 5.5 and b = 4.2, what are (a) the z component of a x b , (b) the z component of a x c , and (c) the z component of b x c ?

Question

With vectors a = 5.5 and b = 4.2, what are (a) the z component of a x b , (b) the z component of a x c , and (c) the z component of b x c ? 
The angle between a and b is 90 degrees.