So, sine of theta, let me write it over here, sine of theta at time t sub naught, that's what we care about, t is equal to t sub naught, what's that going to be? Well, sine is opposite over hypotenuse, so that's going to be y at t sub naught over our hypotenuse of 20 meters. Well, that's going to be equal to, that's going to be equal to, they tell us y of t sub naught is 15 meters over 20 meters, which is the same thing as 3 4ths. So, by this yellow information, they actually told us that this right over here is going to be equal to 3 4ths. So, this times 3 4ths times the rate of change of theta with respect to t. And so, now we just solve for this, and we're done. So, this is going to be, what's negative 20 times 3 4ths? That is negative 15, that is negative 15.