A computer $A$ generated some data that can only be either $0$ or $1$. The data was sent over local network to computer $B$, which sends it to computer $C$, which consequently sends it to computer $D$. Taking the noises into consideration, the probability of the data getting transferred from one computer to another unchanged is just $35\%$. If it is known that the data that was generated by computer $A$ got correctly to computer $D$, find the probability that computer $B$ received the correct data.
Any tips on how should I start? What's the idea here and how can I interpret the known fact that computer $D$ received the correct data?