Answer
$7.3mm$
Work Step by Step
We know that
$d_i=-md_{\circ}$
$d_i=-(0.035)(10.0)=-0.35cm$
The focal length is given as
$f=(\frac{1}{d_{\circ}}+\frac{1}{d_i})^{-1}$
$f=(\frac{1}{10.0}+\frac{1}{-0.35})^{-1}=-0.363cm$
Now the radius can be determined as
$R=2|f|=2(0.363cm)=7.3mm$
