ANSWER
[tex]3.07876rad\/s^2[/tex]
EXPLANATION
To find the average angular acceleration, we have to find the difference in the angular speeds and divide it by time:
[tex]\alpha=\frac{\omega_2-\omega_1}{t}[/tex]
Therefore, the angular acceleration is:
[tex]\begin{gathered} \alpha=\frac{8.5\pi-3.6\pi}{5} \\ \alpha=\frac{4.9\pi}{5} \\ \alpha=3.07876rad\/s^2 \end{gathered}[/tex]
