Step 1 :Define the function \(S(t) = 0.89 \cdot t^{0.97}\) where \(S(t)\) is measured in billions of dollars and \(t\) is measured in years.
Step 2 :Calculate the total spending from 2005 to 2011 by integrating the function \(S(t)\) from \(t=1\) to \(t=7\).
Step 3 :Calculate the average spending per year by dividing the total spending by the number of years, which is 7.
Step 4 :The projected average spending per year on these ads between 2005 and 2011 is approximately \$2.92 billion per year.
Step 5 :\(\boxed{2.92}\) billion dollars per year is the final answer.