Where does it intersect the y-axis here? Well, when t is equal to zero, the value of this equation is going to be 91, because it intersects our graph right at that point, that point zero comma 91, plus 91. So what is our derivative of h with respect to t at time t equals zero, right at this point right over here? Well, we just have to look at this. You could also write this as h prime of t right over here. So if we want to think about h prime of zero, that's going to be equal to negative 1 1⁴ times h of zero minus 27. What is our initial temperature minus 27?