What this question is trying to get you to understand is that any two ordered pairs that lie on a line are needed to calculate the slope of the function or line itself. So, the formula for calculating the slope of any line is
the second "y-value" minus the first "y-value" divided by the second 'x-value" minus first "x-value".
Now you have already been given one ordered pair that lies on the line but you need two for this equation. So plug in any x value and solve for y to get the y value. These two answers, the x you plugged in and the result, y, will be the second ordered pair, (x,y). Now take the two ordered pairs (9,-5) and your (x,y) and use the formula above. The cool thing about this equation is you can choose which ordered pair to use first and second it doesn't matter. Now understanding this, we take the equation and come up with the slope,
Plug in the x and y values you came up with in the equation, and remember they can be ANY values that make the equation true, and you should have your slope for this particular line. Hope I could help!