Question 426007
The best place to start is the idea that the "=" sign is like
a balance point, and whatever you do to one side, you
must also do to the other side to keep the balance.
If I start with:
{{{ 7 = 7 }}}
This is balanced
Now if I add {{{1}}} to just one side, I get
{{{ 8 = 7 }}}
This is unbalanced
But if I now add {{{1}}} to the other side,
{{{ 8 = 8 }}}
It's back in balance
This rule applies to addition, subtraction, 
multiplication, and division