7m+8=8m
7m-8m= -8
Whenever you move a number for the opposite side , you change the sign. For example, the number is 6 , then you move it to the other side. The sign becomes negative 6.
-m=-8
The m cannot be a negative sign. So you multiply it by -1 and for -8.
-1(-m)= -1(-8)
m= 8
Double check answer if you want to:
7m+8=8m
Substitute the answer for m.
7(8)+8=8(8)
64=64
So the answer is correct. m=8