I'm so horrible with %'s, someone please help?

A computer virus is spreading by attatching itself to emails, a user recieves a joke that he decides to forward to eveyone in his address book. Each of the 50 people in his addy book also decide to m forward the joke. If 20% of these 50 people have 30 people in their own book. And 80% of the 50 people have 40 people in their books, how many computers will be affected by the virus? ume none of the 50 people know each other.