How to solve for distance of object with a concave mirror?

[AngelLegs]

Homework Statement

An object is placed a distance do in front of a concave mirror with a radius of curvature r = 6 cm. The image formed has a magnification of M = 4.3. Solve for the object's distance.

Homework Equations

M = -d_i/d_o
(1/d_o) + (1/d_i) = 2/R = 1/f

The Attempt at a Solution

I've tried to rearrange the magnification equation and sub it into the spherical mirror equation in order to cancel out the d_i's, so I can solve for d_o using radius and magnification, except I'm still not even entirely sure how you would manage to make this work.
How would I rearrange these equations to solve for d_o?

 

[FranzDiCoccio]

Have you tried solving for 1/d_i? I mean, find that in the first equation and plug it in the second. From there it should be easy.