$($b$)$ Implement the function $f(A,B,C,D)={\displaystyle \underset{?}{\overset{?}{}}}(0,2,7,8,12,15)$ with don't care conditions $(5,11,14)$ using two $4-$line to $1-$line multiplexers and one $2-$line to $1-$line multiplexer and $C$ as data variable.