A rocket is launched into the air. The height h(t), in yards, of the rocket is a function of time, t, in seconds, as shown in the following table.
t h(t)
0 0
1 20
2 28
3 33
4 28
5 20
6 0

What is the rocket's average rate of change from 3≤t≤6 in yards/second?
Enter your answer as a number, like this: 42
Please help