Chen, Li, Zhang, and Wang were all friends at school. Subsequently each of the 6 subpairs meet up; at each of the six meetings the pair involved quarrel with some fixed probabilityp, or became firm friends with probability 1 -p, Quarrels take place independently of each other. In future, if any of the four hears a rumour, then she tells it to her firm friends only. If Chen hears a rumour, what is the probability that:

(a) Wang hears it?

(b) Wang hears it if Chen and Li have quarrelled?

(c) Wang hears it if Li and Zhang have quarrelled?

(d) Wang hears it if she has quarrelled with Chen?