3y = 18

We want to get it in the form

 y = mx + b

Divide both sides by 3 to solve for y

3y = 18
 y = 6

Now there is no "mx" term but we can insert "0x"
without changing the value, so we do that:

 y = 0x + 6

Now we can compare that with

 y = mx + b

and we see that m = 0, so the slope is 0.

That means the line is horizontal:



Edwin