I suspect that you are missing a factor of x. Let's say that the x is with the 9 so that y - 9x = 17. Then, you need to put your equation in slope-intercept form: y = mx + b. this equation says that the slope is ALWAYS in front of the variable when the x-term is on the right hand side and y is on the left hand side.
So, we add 9x to both sides to move the x-term over the right. We have y = 9x + 17. Now, compare
y = mx + b
y = 9x + 17
We see that 9 is in front of x and that is the slope!
However, if there is no x, then what you have is y = constant, which is a horizontal line. The slope of a horizontal line is always zero because it does not rise.