Answer
$d_i=60.0cm$ (image in front of the mirror)
Work Step by Step
We know that
$f=\frac{1}{2}R$
$\implies f=\frac{1}{2}(40.0)=20.0cm$
Now we can find the image distance as
$d_i=(\frac{1}{f}-\frac{1}{d_{\circ}})^{-1}$
We plug in the known values to obtain:
$d_i=(\frac{1}{20.0}-\frac{1}{30.0})^{-1}=60.0cm$ (image in front of the mirror)
