regula de 3 compusa sau reducerii la unitate
6m.........10z.........420m
6m............1z.........x
x=420*1/10=42
6m............1z.........42m
1m............1z.........y
y=42*1/6=7m
1m............ 1z.........7m
10m............8z.........z
z=7*10*8=560m