A passenger who normally travels from Cambridge to Leicester on the 17:00 train finds that engineering work means he has to catch a bus instead. He needs to catch a
connection from Leicester and normally has 20 minutes to spare, although 10 minutes
are sufficient to allow him to catch the connection. His 60 mile journey to Leicester
normally takes 110 minutes. The bus journey is 25% further and the average speed of
the bus is 30 miles per hour. Buses leave every 15 minutes after 15:55.
Which bus should he catch to ensure that he arrives at Leicester no more than 20
minutes and no less than 10 minutes before his connecting train?