We could write this as the rate of change of the number of words we know with respect to time. Or we could use the alternate notation. We could say this is w prime of t. Either way, it's going to be equal to this thing. It's negative, let me do that same color. It's equal to negative 16 times one minus 0.1t. So what's this going to be? What is the rate of change of the number of words known per day two days after studying for the test?