s=v₁*t₁ - z prądem rzeki
s=v₂*t₂ - pod prąd
s=(vs+vrz)*t₁ [v₁=(vs+vrz)]
s=(vs-vrz)*t₂ [v₂=(vs-vrz)]
45min=0.75h
75min=1.25h
18=0.75vs + 0.75vrz
18=1.25vs - 0.75vrz
0.75vs + 0.75vrz=1.25vs - 0.75vrz
0.5vs=1.5vrz
vs=3vrz
18=0.75vrz+0.75*3vrz
18=3vrz
vs=6km/h
vs=vrz*3
vs=18km/h
