As part of an assessment of the role of organized activities for your user base, you have compiled the following facts regarding attendance at the most recent User Conference and subsequent software license renewal. The universe you are studying consists of all users with an active license at the time of the conference. The probability of a user attending the conference was 0.13. The probability that a user attended the conference and renewed their license was 0.11. The probability that a user neither attended the conference nor renewed their license was 0.24. 

a. Draw a probability tree for this situation. 

b. Given that they attended the conference, what is the probability that they renewed their license? 

c. Given that they did not attend the conference, find the probability that they renewed their license. 

d. Did those who attended the conference renew their licenses at a higher rate than those who did not? How do you know?