b
\(\begin{array}{l}
 - \left( {g + \gamma {v^2}} \right) = \frac{{dv}}{{dt}}\\
 - gdt = \frac{g}{\gamma }\left( {\frac{{dv}}{{\frac{g}{\gamma } + {v^2}}}} \right)\\
{\rm{integrating}}\,0\, \to \,t\,and\,{V_0} \to 0:
\end{array}\)

\(\begin{array}{l}
 - gt =  - \sqrt {\frac{g}{\gamma }} {\tan ^{ - 1}}\left( {\frac{{{V_0}}}{{\sqrt {\frac{g}{\gamma }} }}} \right)\\
t = \frac{1}{{\sqrt {\gamma g} }}{\tan ^{ - 1}}\left( {\frac{{\sqrt \gamma  }}{g}{V_0}} \right)
\end{array}\)