\(\frac{1}{f}=\frac{n_2-n_1}{n_1}(\frac{1}{R_1}-\frac{1}{R_2})\)

\(\frac{1}{25}=\frac{1.52-1}{1}(\frac{1}{\infty}-\frac{1}{R_2})\)

\(R_2=-13cm\)