A concave mirror forms a real image twice as large as the object. The object is then moved such that the new real image produced is three times the size of the object. If the image was moved 94.1 cm from its initial position, how far was the object moved?

Question

A concave mirror forms a real image twice as large as the object. The object is then moved such that the new real image produced is three times the size of the object. If the image was moved 94.1 cm from its initial position, how far was the object moved? 
I have no clue how to start this...

Steve · Answer

this should help http://farside.ph.utexas.edu/teaching/302l/lectures/node137.html