Experts please tell that how m-4n=1 and m-6n=-1 has come in the second last step.....please explain it in a bit detail.

Find the values of m and n for which the following system of linear equations has infinitely many solutions
3x + 4y = 12
(m + n)x + 2(m – n)y = (5m – 1)
 

Dear Student,

Solving from the last third step
4(m+n) = 5m-1 and (5m-1) = 6(m-n)
=> 4m + 4n  = 5m - 1 and 5m - 1 = 6m - 6n
=> (4m + 4n) - 4m = (5m -1) - 4m and 6n + (5m-1)-5m = 6n + (6m-6n) - 5m      
=> (4n)+1 = (5m-4m -1) +1 and 6n-1 = 6m-5m
=> 4n+1 = m and 6n-1 = m
=> m-4n = 1  and m-6n = -1

Regards