We want the equation of the tangent line, which might look something like this, at t equals zero. So this thing would be of the form y is equal to the slope of the equation of the tangent line. Well, it would be the derivative of our function at that point, so dh dt, times t, plus our y-intercept. 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.