Answer
$R=72cm$
Work Step by Step
To find the radius of curvature, use the equation $$R=2f$$ "The distance between the focal point and the mirror" is defined as the focal length. Therefore, the focal length is $36cm$. Since the mirror is concave, the value of the focal length is positive. Substituting this value into the equation yields $$R=2(36cm)=72cm$$