The average rate of change of a function is given by the following formula.

Where a = 3 and b= 11.
First, evaluate the function when x = 3.

This means f(a) = 13.
Second, evaluate the function when x = 11.

This means f(b) = 29.
Once we have all the values we need, we can find the average rate of change using the formula.

Therefore, the average rate of change is 2.