So pause this video and I encourage you to write it out. What do you think this means? And be sure to include the appropriate units. All right, now let's do this together. If d is equal to the distance driven, then to get d prime, you're taking the derivative with respect to time. So one way to think about it is, it is the rate of change of d. So we could view this as d prime is going to give you the instantaneous rate. And they are both functions of t. So one way to view d prime of two is equal to 100, that would mean, well, what is our time now?