Answer :
The average acceleration can be written as:
[tex]a=\frac{\Delta v}{\Delta t}[/tex]Then, for our case, we can find out the time taken by applying:
[tex]\Delta t=\frac{\Delta v}{a}\rightarrow\Delta t=\frac{39}{6}=6.5s[/tex]Then, the total time taken is equal to 6.5s