Use to find the y intercept (b).
So the equation would be
I suppose you would put -2 in the first box and 20 in the second one.
I'm not sure what the y = box and the x = box means unless they want the x and y intercepts. If that's the case, the y-intercept we just found would be 20 and if you set y = 0 in the equation we defined, we would get an x-intercept of 10. But the original question didn't ask for that, so I don't know what they expect there.