Species A: GÂ TÂ TÂ GÂ AÂ GÂ CÂ TÂ AÂ GÂ TÂ AÂ TÂ GÂ GÂ AÂ CÂ C
Species B: GÂ AÂ TÂ AÂ AÂ GÂ CÂ TÂ AÂ GÂ TÂ AÂ AÂ GÂ GÂ TÂ CÂ A
Differences: Â Â 1 Â Â 1 Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â 1 Â Â Â Â 1 Â Â 1
In comparing the species, Â I noticed 5 differences. I noted the differences using 1.Â
Since the problem states that 1 mutation occurs per 15 million years, it is safe to say that the two species shared a common ancestor 75 million years ago.
5 mutations * 15million yrs/mutation = 75 million years.