$($a$)$ Construct NFA's A and $B,$ such that $L(A)=L(a{b}^{*}{a}^{*}),$ and $L(B)=L(a^{*}{b}^{*}a).$

Then use these NFA's to construct an NFA $C,$ such that $L(C)=L(A)L(B).$