Răspuns:
x=drumul
10/100dinx=x/10 a parcurs prima zi
30x/100=3x/10 a parcurs a2a zi
x/10+3x/10+¹⁰⁾42=¹⁰⁾x
x+3x+420=10x
420=10x-4x
x=420:6
x=70km are drumul
verificare:
70:10=7 km a parcurs in prima zi
3·70:10=21 km a parcurs a2a zi
7+21+42=70 km lungimea drumului