Answer
(a) $-43cm$
(b) $43cm$
Work Step by Step
(a) We can find the focal length of the convex side as
$f=-\frac{1}{2}R$
$\implies f=-\frac{1}{2}(0.86)=-43cm$
As it is the convex mirror, the focal length is negative.
(b) We can find the focal length of the concave side as
$f=\frac{1}{2}R$
$\implies f=\frac{1}{2}(0.86)=43cm$