This is just the product rule here, plus the first function, b of t, times the derivative of the second function with respect to time. And we need to figure out not just the general expression, they want us to know what the rate of change of the area, so a prime of t at that instant, at t sub zero. So what we wanna figure out, we wanna figure out a prime at time t sub zero. Well, that's just going to be equal to 1 1 2 times b prime of t sub zero times h of t sub zero plus b of t sub zero times h prime of t sub zero. Now, this might seem daunting, except they've given us a lot of this information. What is b prime of t sub zero? Well, they tell us the rate of change of b with respect to time, and it seems like it's just gonna stay at negative 13 meters per hour, so they gave us this.