-6=b/18
To simplify this, isolate the variable. (get the "b" all by itself)
to get b/18 all by itself, you must "undo" the division by 18.
That would mean multiply both sides by 18.
-6 * 18 = b/18 * 18
Which gives you -6 * 18 = b, and b calculates to -108.
Whatever you do to one side of the equal sign, you must do the other side to maintain the state of equality.
I hope this was helpful, and if you need more explanation, speak up. - LambLamb