The additive inverse is 2/7....I think
x = -3 if its vertical.
The slope is up 1 over 0 (1/0) so it is undefined.
You'd have to work out the gradient y=mx+c is the equation of a line, where m is the gradient, c is the y intercept (where the line cuts through the y axis) x is the x coordinate of the graph and y is the y coordinate on the graph