The time taken by the rocket sled is 3 s.
Given data:
The acceleration of the rocket sled is a=15.0 m/s².
The initial velocity is u=10.0 m/s.
The final velocity is v=65.0 m/s.
The expression for the acceleration is given by,

Here, t is the time taken.
Substitute the given values in above equation to calculate the time,

Thus, it will take 3 s to attain the required acceleration.