Answer
$S_{0}=37.5~cm$
Work Step by Step
Given
$\frac{1}{f}=\frac{1}{S_{0}}+\frac{1}{S_{i}}$
$f=15cm, S_{0}=?, S_{i}=25cm$
$\frac{1}{15}=\frac{1}{S_{0}}+\frac{1}{25}$
$\frac{1}{S_{0}}=\frac{1}{15}-\frac{1}{25}$
Therefore, $S_{0}=37.5~cm$
How to use the calculator:
$15,*,x^{-1},-,25,*,x^{-1},=,x^{-1},=.$
