250, and this is because of probability. Since half of the numbers are odd numbers, and half are even. It would be hard to determine, your probability would be 1/2. 1/2 of 500 is going to be 250.
This is in slope-intercept form, so you can think of it as being y=mx+b. Invert m (the slope) and flip its sign, and then substitute the x and y values in and solve for b. The answer is y=7/2x-20.
