Well, this is 0.36 plus 0.64 is equal to s squared. This is 1 is equal to s squared. And we only care about positive distances, so we have s is equal to 1 right now. So we also know what s is. So let's substitute all of these numbers in and then try to solve for what we came here to do, solve for ds dt. So the rate at which 2 times x, maybe I'll do that in yellow, 2 times x, x is 0.6, is going to be 1.2 times dx dt. So that's negative 30 miles per hour.