Where does the graph of y=-3x-18 intersect the x-axis?

When a graph of any form of equation intersect the x-axis, this automatically means that y = 0. And then we solve for x to find the coordinates of the point of intersection, or just the value of x.
y = -3x - 18
-3x - 18 = 0
We add 18 in both sides so we can get the variables on a side and the numbers on the other:
-3x - 18 + 18 = 0 + 18
-3x = 18
Then you divide each side by -3 to get x alone on a side and its value on the other:
(-3x)/-3 = 18/-3
x = -6.

So the graph of y= -3x-18 intersect the x -axis when y=0 and x=-6.

(I've added a picture of the graph of y= -3x-18 under the answer)

Hope this Helps! :)