Use Newton's second law of motion. I'm sure I don't have to tell you
what it says, but I will anyway:
Force = (mass) times (acceleration) .
The question GIVES you two of those numbers, and asks you to find
the third one.
Write the numbers you know into Newton's equation:
2000 N = (mass) times (2.2 m/s²)
Divide each side of that equation by 2.2 m/s², and
what you'll have left will be the mass, in units of kg.