Notam cu x lungimea traseului
[tex]\it Etapa\: I\\\\\\\dfrac{2}{3}x-20=\dfrac{2x-60}{3}[/tex]
Cat a mai ramas din traseu dupa ce a parcurs prima etapa?
[tex]\it x-\dfrac{2x-60}{3}=\dfrac{3x-2x+60}{3}=\dfrac{x+60}{3}\:\:\:\text{\it rest din traseu}[/tex]
[tex]Etapa\:\:II\\\\\\\dfrac{x+60}{\not3}\cdot\dfrac{\not3}{5} +15=\dfrac{x+60+15\cdot5}{5}= \dfrac{x+135}{5}[/tex]
[tex]\it Etapa\:\:III\\\\65 km[/tex]
[tex]\it \dfrac{2x-60}{3} +\dfrac{x+135}{5} +65=x\:\:|\cdot15\:\text{\it(inmultim toata ecuatia cu 15)}[/tex]
[tex]\it 5\cdot2x-300+3x+405+975=15x\\\\10x-300+3x+405+975=15x\\\\13x+1080=15x\\\\1080=15x-13x\\\\1080=2x\\\\x = 1080:2\\\\\boxed{\it x=540\: km}[/tex]
Răspuns: 540 km