1/3 din x=x/3 prima etapa
x-x/3=(3x-x)/3 =2x/3 restul
a doua etapa 1/4 din rest=1/4*2x/3=x/6
noul rest
x-x/3-x/6=(6x-2x-x)/6=3x/6=x/2
a treia etapa 1/3 din x/2=x/6
x/3+x/6+x/6+12=x
x/3+2x/6+12=x
x/3+x/3+12=x
x-2x/3=12
x=12×3
x=36 km are lungimea drumului
verificare
x/3+x/6+x/6+12=x
12+6+6+12=36
36=36