So, Since the function at this point x=100 can be approximated by a line of this slope,
This problem is stupid. It's two and a half times harder than just plugging in the two values outright and it's off by about 2%
Also this question which I kind of know how to do but can't get anywhere:
The profit P for a cerain manufacturer selling x items is
P(x) = 200xe^(-x/400)
Use calculus to estimate the change in P as the number of items changes from x=100 to x=105 items.