21 because first of all let’s start with the fact that 5 years ago a was 8m. Let’s substitute 1 for m if m was one, a would be 8 (five years ago) both add 5, but 13 would not be 3 times older than 6. Let’s then substitute m for 2. Then a would be 16 because 8*2 equals 16. Both add 5 and you get 21 and 7. 21 is 3 time more than 7.
