So if you take the derivative with respect to time, that's going to give you v prime, and these are all functions of t. These are all functions of t. And they say at t equals seven, it's equal to negative three. So this, which is the same thing as the slope of tangent line slope of tangent, tangent line, and they tell us that v prime of, at time equals seven minutes, our rate of change of volume with respect to time is equal to negative three. And so you could say, if we were to write it out, this means that after, after seven minutes, seven minutes, the tank is being drained at an instantaneous, instantaneous. That's why we need that calculus for that instantaneous rate. At an instantaneous rate of, now, you might be tempted to say it's being drained at an instantaneous rate of negative three liters per minute. But remember, the negative three just shows that the volume is decreasing. So one way to think about it is, this negative is already being accounted for when you're saying it's being drained.