7. Suppose a binary digit (0 or 1) needs to be transmitted across a series of 4 channels. Each time, the digit is transmitted correctly to the next channel with probability 0.9, and is transmitted incorrectly (meaning that 1 is transmitted as 0, and 0 is transmitted as probability 0.1. If the digit 0 is sent, what is the probability that the digit that is received (after having been transmitted across the 4 channels) is a 0? 1) with