What is the rate of change of the number of words known per day two days after studying for the test? Well, we just have to evaluate this when t is equal to two. So w prime of two, do that in magenta. W prime of two is going to be equal to, whoops, I'll just go with the magenta, is equal to negative 16 times one minus 0.1 times two. Times two, close parentheses. And that's going to be equal to, well let's see, what is this? This is one minus, essentially 0.2, this is going to be 0.8.