Velocity question

A spacecraft travels away from a celestial body, with the engine off and with velocity v>0. At the time t1 the rear rockets are turned on, obtaining an acceleration a=+20m/s², and are turned off at t2=t1+5s, reaching speed v’.
How much speed did the spacecraft gain?
Answer: 360km/h

Hi everyone,
i can’t seem to find the right answer, thank you for your help!