Last year's match at Wimbledon between John Isner and Nicolas Mahut, which lasted 11 hours and 5 minutes, set a record for the
longest match in tennis history. The fifth set of the match lasted 8 hours
and 11 minutes. Approximately what fraction of the whole match was
taken up by the fifth set?

A) 1/5
B) 2/5
C) 3/5
D) 3/4
E) 9/10

(with working out please)