Simpsons rule problem. why is this equation setup this way?

Question

I am a bit confused as to why a problem in my book is using A(t) instead of D(t) in teh setup for simpsons rule. Why is the integral at the end setup like:

$$\int_0^43200 A(t)dt$$ and not $$\int_0^43200 D(t)dt$$

Here are the passages:

Answer 1

You're right, it's a typo and they should be integrating $D$ not $A$, as $A'=D$ by definition (and $A$ is the amount of data transmitted by time t so integrating $A$ wouldn't help solve the question). It's just a typo in the textbook, nothing more.