And then finally, when time is 40, her velocity is 150, positive 150. So at 40, it's positive 150. And so these are just sample points from her velocity function, but what we wanted to do is we wanted to find, in this problem, we wanted to say, okay, when t is equal to 16, what is the rate of change? And we don't know much about, we don't know what v of 16 is, but what we could do is, and this is essentially what we did in this problem, we could say, all right, well, we can approximate what the function might do by roughly drawing a line here. So if you draw a line there, and you say, all right, well, v of 16, or v prime of 16, I should say, so v prime of 16 is going to be approximately the slope, is going to be approximately the slope of this line. That's going to be our best job, based on the data that they've given us, of estimating the value of v prime of 16. So we literally just did change in v, which is that one, delta v, over change in t, over, over delta t, to get the slope of this line, which is our best approximation for the derivative, when t is equal to 16.