v₁=80 km/h
S₂=40 km
t₂=45 min = 0,75 h
S=S₁+S₂=120 km
S₁=S-S₂=120-40=80 km
[tex]t_1=\frac{S_1}{v_1}=\frac{80 \ [km]}{80 \ \frac{km}{h}}=1 \ h[/tex]
[tex]v_{\'sr}=\frac{S}{t}=\frac{S_1+S_2}{t_1+t_2}=\frac{120 \ [km]}{1+0,75 \ [h]}\approx68,57 \ \frac{km}{h}[/tex]
