Exploit RSA , given some information about n
The question spezifies $n_1 = p*q_1$, $n_2 = p*q_2$. With that we can calculate $gcd(n_1,n_2) = p$ which lets us solve $n_1 / p = q_1$ and $n_2 / p = q_1$. Now we have every information needed to calculate the private part of Bob's key and thereby decrypt all messages sent to him.