y is decreasing. The bird is diving down to get its dinner. So times 20 feet per second, so that's that right over there, plus 10 times dy dt. 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.