20m - n = p
Add n to both sides:
20m = n + p
Add m to both sides:
21m = n + p + m
Now, divide both sides by 3
7m = (n + p + m)/3 = the average of n, p, and m
If 20m − n = p, then which of the following represents the average (arithmetic mean) of m, n, and p, in terms of m?

1) 2m −1
2) 4m
3) 6m
4) 7m
5) 6m/5