( \(\mu_{1}\) is refractive index of lens and \(\mu_{2}\) is of surrounding medium)
\(1.25=\left(1.5-\mu_{2}\right)\left(\frac{1}{0.2}+\frac{1}{0.4}\right)\)
\(\frac{1.25 \times 0.08}{0.6}=\left(1.5-\mu_{2}\right)\)
\(\Rightarrow \mu_{2}=\frac{4}{3}\)