Please explain this question ....in this question how expectance of y is 1/2 . pls show steps and can't we do e(x/z) in other way ...pls show steps

dear, according to me, the (x,y)=(0,1) given in the question so the probability of y is 1/2( as no of y values is 1/(total no of values i.e 2)).. from this we get probability of y ...