so the equation we are working with is y=mx +b. If you use the distance formula, you will find the slope. The slope is 1/2 and the y intercept is 0. your equation is y=1/2x. So plug in the point that it gives you.
-2 is your y value.
so it will look like this: (x could also be n)
-2=1/2x...solve....n=-4