x-nr de km parcursi de calatori<br />x/3-nr de km parcursi in prima zi<br />(x-x/3)/4-nr de km parcursi in a doua zi<br />18-km parcursi in a treia zi<br />x=x/3+(x-(x/3))/4+18<br />x=4x/12+(3×(x-x/3))/12+18<br />12x=4x+3×(x-x/3)+216<br />12x=4x+3x-x+216<br />12x=6x+216<br />6x=216
x=216/6
x=36