[tex] Viteza = \dfrac{distanta}{timp} \\ \\
\rightarrow 840m = 0,84 = \dfrac{84}{100}~km \\ \\
\rightarrow 20 minute = \dfrac{1}{3}h~~(ore) \\ \\ \\ \\
V = \dfrac{84}{100}\cdot 3 = \dfrac{252}{100} = \boxed{2,52~km/h} [/tex]
840 m -------- 20 minute
x m ------------ 60 minute
x = 840 x 60 : 20 = 2520 m
v = 2520 m / h = 2,52 Km/h