b)80min=60min+20min=1ora+20min
4-1h20min=2si40min( ora la care a pornit biciclistul)
c)24:00-21:30=2:30 (timpul care trece pana la miezul noptii)
2:30+ 48:00(2 zile)=50:30
56:00-50:30=5:30(ora la care ajunge trenul in gara, in a treia zi de la plecare,adica joi)
d)lectia dureaza 3/4din 60=45min
pauza dureaza 1/6 din 60=10min
8:00+0:45+0:10+0:45+0:10+0:45+0:10+0:45+0:10+0:45=12:25