Chang the trainer has two solo workout plans that he offers his clients: plan a and plan b. each client does either one or the other (not both). on friday there were 5 clients who did plan a and 3 who did plan b. on saturday there were 7 clients who did plan a and 9 who did plan b. chang trained his friday clients for a total of 6 hours and his saturday clients for a total of 12 hours. how long does each of the workout plans last?