"You don't need a taxi."
Translation:Tú no necesitas un taxi.
Marion, it's from the verb necesitar - to need.
If you remember your present tense verb conjugations:
yo necesito - I need
tú necesitas - you need
él necesita - he needs
usted necesita - you need
ella necesita - She needs
ellos necesitan - they need
So, tú no necesitas un taxi - you don't need a taxi.
It could also have been usted no necesita un taxi, 'you don't need a taxi' using the Usted you formal form.
Just don't forget to match the conjugations correctly:
tú necesitas, usted necesita
i wrote "no necesitas un taxi" and it was marked wrong that it should be "no precisa un taxi"! something isnt right