Bonjour,

60mn -> 40km

1mn -> 40/60

8mn -> (40*8)/60

=>5,33km

60mn -> 80km

1mn -> 80/60

4 mn -> (80*4) / 60

=>5,33km

5,33 + 5,33 = 10, 66 => 10,7km

12mn -> 10,7 km

1mn -> 10,7/12

60mn -> (10,7*60)/12

=>53,5km/h