So this is going to be in meters. If we say b prime of t, this is going to be how much our base is changing with respect to time. So this is going to be meters per, and they give us right over here, they say it's decreasing at a rate of 13 meters per hour. So the units here are meters per hour. And so b prime of t, that is going to be in meters per hour. A at time t sub zero. Remember, a is the area of our triangle, and we're measuring everything in meters, as you can tell from the information they've given us.