I have a hunch that you've got the question totally covered, and what you actually need is the answer.
- Kinetic energy = (1/2) (mass) (speed²)
Multiply each side by 2 : 2 x KE = (mass) ( speed²)
Divide each side by (mass): Speed² = 2 x KE / mass
Square root each side: Speed = √(2 KE/mass)
Look at that ! The question GIVES you the KE and the mass. All you have to do is plug those 2 numbers into the right side of that equation, turn the crank, do the arithmetic, and the speed falls out.
I get 200 m/s . You need to check my work.
(IF that's correct or anywhere close, it's equivalent to something around 447 miles per hour, which is very reasonable for a cruising airliner.)