Given
f = 20 cm
\(u_1=-25\)
\(u_2=-50\)
when u = -25
\(\frac 1f=\frac 1v-\frac 1u\)
\(\frac 1v=\frac 1f+\frac 1u\)
\(\frac 1v=\frac{1}{20}+\frac{1}{(-25)}\)
\(\frac 1v=\frac{5-4}{100}\)
\(\frac 1v=\frac{1}{100}\)
v = 100 cm
\(m_1=\frac{-v}{u}\Rightarrow \frac{-100}{-25}=4\)
when u = -50
\(\frac 1f=\frac 1v+\frac 1u\)
\(\frac 1V=\frac {1}{20}-\frac{1}{50}\)
\(\frac 1V=\frac{5-2}{100}\)
\(\frac 1V=\frac{3}{100}\)
\(V = \frac{100}{3}\)
\(m_2=\frac{-v}{u}=\frac{\frac{100}{3}}{50}=\frac 23\)
\(\cfrac{m_1}{m_2}=6.\)