Answer
(a) $0$.
(b) $0$.
Work Step by Step
(a) It is clear that the cross product of a vector and itself is zero, that is, $$\langle 4,8,2\rangle\times \langle 4,8,2\rangle =0.$$
(a) It is clear that the cross product of a vector and its multiple is zero, that is, $$\langle 4,8,2\rangle\times \langle 2,4,1\rangle =2\langle 2,4,1\rangle\times \langle 2,4,1\rangle =0.$$
