ANSWER:
4.3 seconds
STEP-BY-STEP EXPLANATION:
We have that the force is determined in this case by the following formula:
[tex]F=m\cdot\frac{\Delta v}{\Delta t}[/tex]We know all the values except time, therefore we can calculate time by substituting and solving for time like this:
[tex]\begin{gathered} 15=20\cdot\frac{3.2-0}{\Delta t} \\ \Delta t=20\cdot\frac{3.2-0}{15} \\ \Delta t=4.3\text{ s} \end{gathered}[/tex]The time would be 4.3 seconds
