So lets do this like
8m + 4 - m = 7m + 3 - 3m - 16
firts arrange them with their likes
8m - m + 4 = 7m - 3m + 3 - 16
now add or subtract
7m +4 = 4m - 13
now again change their places
7m - 4m = -4 - 13
when we bring a value to the other side of equal sign we also change its own sign!
3m = - 17
m = - 17/3
any probs......feel free to ask!