Answer
$19.8cm;-63.0cm$
Work Step by Step
The focal length of the convex lens can be calculated as
$\frac{1}{f_1}=\frac{1}{d_{\circ 1}}+|frac{1}{d_{i1}}$
We plug in the known values to obtain:
$\frac{1}{f_1}=\frac{1}{42cm}+\frac{1}{37.5cm}=19.8cm$
The object distance to convex the lens is $d_{\circ 2}=15cm-37.5cm=-22.5cm$
Now the focal length of the concave lens is given as
$\frac{1}{f_2}=\frac{1}{d_{\circ 2}}+\frac{1}{d_{i 2}}$
We plug in the known values to obtain:
$\frac{1}{f_2}=\frac{1}{-22.5cm}+\frac{1}{35cm}$
$\implies f_2=-63cm$
