Solve for the missing coordinate to equal the slope undefined
(x,-5) and (-9,3)

For the slope of a line to be undefined, it must be going straight up, making all points have the same x-value. Because of this, for this line to be undefined, x must equal the x of your second point, or -9. This makes your answer x=-9.

20000 as first it increases by 2500 then by 5000 so next it will increase by 10000