So plus 10 times negative 20 feet per second. And now we just solve for dx dt. So let's see, what do we have? We have 20 times, let's see, let me subtract 15 dx dt from both sides of this equation. And we get 5 dx dts. 5 dx dts, I just subtracted this from both sides of the equation. This is 15 dx dts, this is 20.