Ken is considering entering a local fishing tournament, but his choice to enter depends somewhat on whether his rival, Billy, will enter the same fishing tournament. Ken thinks that he has a $0.4$ probability of winning the fishing tournament if Billy does not enter the tournament, and a $0.15$ probability of winning if Billy does enter the fishing tournament.
If the probability that Billy enters the fishing tournament is $0.40$,
a) find the probability that Ken wins the fishing tournament.
b) If Ken does not win the fishing tournament, what is the probability that Billy did not enter the tournament?
I've trying to set up tree diagram, but does not work in either way need help!