John and Ken are reading a book every 3 days, John reads a book every 7 days and Ken reads a book every 9 days. If they are reading together now, how long take they to read a book together again?
John and Ken are reading a book every 3 days, John reads a book every 7 days and Ken reads a book every 9 days. If they are reading together now, how long take they to read a book together again?