Answer:
a) The speed at the beggining of the interval is 60 words per minute.
b) The maximum speed is 80 words per minute at the instant t = 2 minutes.
c) The average speed over the 6-min interval is 60 words per minute.
Explanation:
a) Find the speed at the beginning of the interval.
This is W(0)

Then

The speed at the beggining of the interval is 60 words per minute.
b) Find the maximum speed and when it occurs.
Suppose we have a quadratic equation in the following format:

The vertex is the point

In which

In this question:

So

Then


The maximum speed is 80 words per minute at the instant t = 2 minutes.
c) Find the average speed over the 6-min interval.
The average value of a function f(x) over an interval [a,b] is:

In this question:

So


So




Then

The average speed over the 6-min interval is 60 words per minute.