>>> from autopistes import trams

---- inici
>>> round(trams(3, 10, 6.5, 50), 2)
45.5
>>> round(trams(10, 3, 6.5, 50), 2)
45.5
>>> round(trams(7, 8, 5, 60),    2)
5.0
>>> round(trams(14, 2, 6.1, 60), 2)
60.0

---- fi