\(\frac{3}{2 V }=\frac{1}{30}\)
\(V =45 \,cm\)
\(\frac{1}{ V }-\frac{3}{\frac{2}{15}}=\frac{1-\frac{3}{2}}{\frac{2}{-15}}\)
\(\frac{1}{ V }-\frac{1}{10}=\frac{1}{30}\)
\(\frac{1}{ V }=\frac{1}{10}+\frac{1}{30}=\frac{4}{30}\)
\(V =7.5\)
\(V =22.5\)
\(v =225 \,mm\)