5 m + 8 c = 81
8 m + 4 c = 68 | ×2
16 m + 8 c = 136
5 m + 8 c = 81
_____________ ( - )
11 m // = 55
m = 55 : 11
m = 5 litri ( o masina)
c = [ 81 - ( 5×5)] : 8
c = (81 -25) : 8
c = 56 :8
c = 7 litri ( un camion)
un camion consuma 7 litri
o masina consuma 5 litri