Make sure you put similar numbers (those with "m" and those without in this case) on one side and the others on the other side (also when you change, change the signs for each one moved to the opposite)
7m -4m - 6m = 7+1+16
- 3 m = 24 -3m/ -3 = 24/-3 (what you do to one side, you do to the other)