For languages A and $B,$ let the shuffle of A and $B$ be the language

$\{\begin{array}{c}w|w=a_1{b}_{1}cdots{a}_k{b}_k\end{array},$ where $a_{1}cdots{a}_k$inA and $b_{1}cdots{b}_k$inB, each $\{$:$a_i,b_{i}in{}^{**}\}$

Show that the class of regular languages is closed under shuffle.