Solving a convex mirror problem

1. The problem statement, all variables and given/known data

Given the following information: convex mirror, focal length (f) = 12.5 metres, height object (ho) = 5 metres, height image (hi) = 1 metre. Find distance object (do) and distance image (di).

2. Relevant equations

1/f = 1/do + 1/di

Magnification= -hi/ho = di/do

3. The attempt at a solution

I found that the magnification is -0.2.

Rearranging the magnification equation I found that di=-0.2do
and that

My intention was to substitute one of the two into 1/f = 1/do + 1/di

I tried to make the denominators equal after substituting in di=-0.2do however my answer was incorrect.

Correct answers are do = 50 metres, di = -10 metres

I don’t understand how to mathematically solve this problem. Any help would be greatfully appreciated.

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