Answer :
The average velocity between 3 and 6 seconds will be found with the following equation:
[tex]\begin{gathered} v=\frac{v2-v1}{t2-t1} \\ v=\frac{36-9\text{ m}}{6-3\text{ }}\text{ (Replacing the values)} \\ v=\frac{27}{3}m/s\text{ (Subtracting)} \\ v=9\text{ }m/s\text{ (Dividing)} \\ \text{The answer is 9 m/s} \end{gathered}[/tex]