Species A: GĀ TĀ TĀ GĀ AĀ GĀ CĀ TĀ AĀ GĀ TĀ AĀ TĀ GĀ GĀ AĀ CĀ C
Species B: GĀ AĀ TĀ AĀ AĀ GĀ CĀ TĀ AĀ GĀ TĀ AĀ AĀ GĀ GĀ TĀ CĀ A
Differences: Ā Ā 1 Ā Ā 1 Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā 1 Ā Ā Ā Ā 1 Ā Ā 1
In comparing the species, Ā I noticed 5 differences. I noted the differences using 1.Ā
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.