2. a) i) Show that the set $\mathbb{Z}_{7}=\{0,1,2,3,4,5,6\}$ is a group under addition modiulo 7. ii) Find the arder of the element 3 in $\mathbb{Z}_{7}$. b) Show that i) the subset $H=\{x \in R: x>0}$ is a subgroup of $\mathbb{R}^{*}$ the group CS.VS. 1420