Yaw installed a new burglar alarm at his home to detect burglary. The alarm
reliably responds to detecting a burglary but also responds to detecting
smoke. Yaw has two neighbours Yaa and Kofi, who have the responsibility to
inform Yaw at work when they hear the alarm. Kofi always calls Yaw when he
hears the alarm, but sometimes he gets confused with the phone ringing
and calls at that time too. On the other hand, Yaa gets distracted with house
chores and sometimes does not hear the alarm when it sounds.

By using Bayesian network, calculate the probability that the alarm has
sounded, but there is neither a burglary, nor a smoke, and Kofi and Yaa both
called Yaw.