D = distanta, t1,v1,t2,v2 = timupl 1, viteza 1, timpul 2, viteza 2
[tex]D = v_1\cdot t_1 = v_2\cdot t_2
[/tex]
[tex]\text{Dar } v_1\cdot t_1 = v_2 \cdot (t_1+4h) \implies \frac{v_1}{v_2}=\frac{t_1+4h}{t_1}[/tex]
[tex]\frac{35}{21} = \frac{t_1+4h}{t_1}\implies 21\:t_1+84\:h = 35\:t_1
[/tex]
[tex]14\:t_1 = 84\:h\implies t_1 = 6h[/tex]
[tex]D = v_1\cdot t_1 = 35\:km/h \cdot 6\:h = 210\:km[/tex]
[tex]D=210\:km[/tex]