\(\frac{1}{f}=\frac{1}{f_1}+\frac{1}{f_2}-\frac{L}{f_1 f_2}\)

\(f=\frac{f_1 f_2}{f_1+f_2-L}=\frac{(20)(-8)}{(20)+(-8)-(15)}=53.33cm\)

\(\frac{1}{s_2}+\frac{1}{s'_2}=\frac{1}{f_2}\)

\(s'_2=\frac{f_2 s_2}{s_2-f_2}=\frac{(-8)(-5)}{(-5)-(-8)}=13.33cm\)

\(tan 2^0=\frac{|h'|}{f}\)

\(|h'|=f*tan 2^0=(53.33cm)*tan 2^0=1.86cm\)