\(\frac{n_1}{s}+\frac{n_2}{s'}=\frac{n_2-n_1}{R}\)

\(\frac{1.5}{5}+\frac{1}{s'}=\frac{1-1.5}{-2.5}\)

\(s'=-10cm\)

\(m=-\frac{n_1 s'}{n_2 s}=-\frac{(1.5)(-10)}{(1)(5)}=3\)