$(a)$ $\begin{array}{*{20}{c}}
{C{H_3} - CH - Br} \\
{|\,} \\
{\,\,\,\,\,\,{C_2}{H_5}}
\end{array}$
$(b)$ $\begin{array}{*{20}{c}}
{\begin{array}{*{20}{c}}
{\,\,Br} \\
|
\end{array}} \\
{C{H_3} - C - C{H_3}} \\
| \\
{\,\,\,\,\,\,\,\,\,{C_2}{H_5}}
\end{array}$
$(c)$ $\begin{array}{*{20}{c}}
{C{H_3}{\mkern 1mu} - CH{\mkern 1mu} - {\mkern 1mu} {\mkern 1mu} C{H_2}Br} \\
{|\,\,\,\,\,\,\,\,\,\,\,\,\,} \\
{{C_2}{H_5}\,\,\,}
\end{array}$
${H_2}C = CHC{H_2}Br\xrightarrow{{NaCN}}Y\xrightarrow[{2.\,{H_3}{O^ + }}]{\begin{subarray}{l}
1.{C_6}{H_5}MgBr\, \\
diethylether
\end{subarray} }Z$