a
\(V_{T} \propto m^{\alpha} \eta^{\beta} r^{\gamma} g^{k}\)

\(M^{0} L^{1} T^{-1}=\left(M^{1}\right)^{\alpha}\left(M^{1} L^{-1} T^{-1}\right)^{\beta}\left(L^{1}\right)^{\gamma}\left(L T^{-2}\right)^{k}\)

\(0=\alpha+\beta \Rightarrow \alpha=1=k\)

\(1=-\beta+\gamma+k \beta=\gamma=-1\)

\(-1=-\beta-2 k\)

\(\Rightarrow V_{T} \propto \frac{m g}{\eta r}\)