A small object is located 30.6 cm in front of a concave mirror with a radius of curvature of 40.9 cm.

So the question is Where will the image be formed?

I thought I use this equation to solve 1/do + 1/di= 1/f

I solved for R by using f=(1/2)R and got 20.45
I then plug that in with all my information. However the answer I get isn't right. What am I doing wrong?