"I walk and you write."
Translation:Ik loop en jij schrijft.
'Je' is actually wrong. You need the stressed 'jij', since you are trying to say in this sentence that there is a difference between what I am doing (I am walking) and what you are doing (You are writing). If the sentence would have been: you walk and (you) write, it would have been 'je loopt en je schrijft'.
I also put 'je'- I was thinking casually that I was walking and you were writing, no special action on either part, not trying to make a point of differentiating between our separate actions or calling attention to anything- 'you were writing', not 'YOU were writing'... Even then, must it still be 'jij'?
'Jullie' is you in plural form, so the verb changes as well. ("Ik loop en jullie schrijven" is accepted)