So they say the base at time t sub zero, the base is a function of time, but they tell us that it is five meters. So this is five meters right over here. Now what about the rate of change of the base with respect to time? Do they tell us that? Well, look right over here. That's actually the first piece of information they gave us. So the base, B of t of a triangle, is decreasing at a rate of 13 meters per hour.