This is 15 dx dts, this is 20. So we have 5 dx dts is equal to, this part right over here is negative 600. And this part right over here is negative 200. So it's equal to negative 800 feet per second. Or negative 800, and actually this will actually be in feet per second. And so dx dt is equal to, dividing both sides by 5, 5 times 16 is 80. So this is negative 160 feet per second.