Answer
$-9.0cm,12cm$
Work Step by Step
(a) We can find the image distance as
$d_i=-md_{\circ}$
We plug in the known values to obtain:
$d_i=-(\frac{1}{4})(36cm)=-9.0cm$
(b) We can find the focal length as
$f=(\frac{1}{d_{\circ}}+\frac{1}{d_i})^{-1}$
We plug in the known values to obtain:
$f=(\frac{1}{36}+\frac{1}{-9.0cm})^{-1}$
$f=-12cm$