x=lungime drum
8=distanta parcursa
a mers 100%-9%=91%
9%x=9x/100=distanta ramasa de parcurs
8+9x/100=x
800+9x=100x
91x=800
x=800/91=8,(79120) km
varianta corectata
x=lungime drum
8=distanta parcursa
9%x=9x/100=distanta pana la sfertul drumului
8+9x/100=x/4
3200+36x=100x
64x=3200
x=50 km
distanta parcursa deja =25%-9%=16%