m/3-3=n+3/6 2n-m/4=3
The original formula is reduced to 2m-n-21 = 0, 2n-m-12 = 0
The solution is: M = 18, n = 15
Given m-2n / N = 3 / 5, find m + n / 5
By
m-2n/n=3/5
The result is n = 5m / 13
m+n=18m/13
Your problem may have different conditions, or M + n / 5m or M + n / 5N
5 out of 12 and 3 out of 4
=14 out of 12 = 7 out of 6