Answer
a) $d=56.4cm$
b) $m_{total}=-0.12$
Work Step by Step
(a) We know that
$d_{i1}=(\frac{1}{f_1}-\frac{1}{d_{\circ1}})^{-1}$
$d_{i1}=(\frac{1}{-7.0cm}-\frac{1}{24cm})^{-1}=-5.42cm$
and $d_{\circ2}=35.0cm+d_{i1}=40.42cm$
Similarly $d_{i2}=(\frac{1}{14.0cm}-\frac{1}{40.42cm})^{-1}=21.4cm$
Now $d=35cm+d_{i2}=35cm+21.4cm=56.4cm$
(b) We know that
$m_{total}=(-\frac{d_{i1}}{d_{\circ1}})(-\frac{d_i2}{d_{\circ2}})$
We plug in the known values to obtain:
$m_{total}=(-\frac{-5.42cm}{24cm})(\frac{-21.4cm}{40.42cm})=-0.12$