You can
put this solution on YOUR website!The basic rule is:
Whatever you do to one side of the (=) sign, you must
do to the other side. When you're done, the left side
is still equal to the right side.
Suppose I say

Is it OK to divide both sides by 3? yes

because any number divided by itself = 1
-----------
F = ma
I can divided both sides by m
F/m = ma/m
This is the same as
F/m = (m/m) x a
and notice m/m = 1, so
F /m = a
That's the answer
Hope this helps