Mike sends many e-mails to his friends each week. The ratio of the number of e-mails he wrote for the last 3 weeks is 4:6:5. If Mike wrote 4 more e-mails on the 2nd week than on the 1st week,
(a) How many e-mails did he write each of the three weeks?
The 1st week: e-mails
The 2nd week: e-mails
The 3rd week: e-mails
(b) If it takes 15 minutes for Mike to write an e-mail, how much time did he spend on writing e-mails during the 3rd week?