I need help solving this sample question:

8. Online chat rooms are dominated by the young. Teens are the biggest users. If we look only at adult internet users (aged 18 and over) 47% of the 18 to 29 age group chat, as do 21% of the 30 to 49 age group and just 7% of those 50 and over. The distribution of age break down for these internet users is: 30% of the adult internet users are 18 to 29, another 50% are 30 to 49 and the remaining 20% are 50 and over. What percentage of adult chat room participants are aged 50 and over? (Reference Examples 4.46 and 4.47, pages 286 and 288, respectively)