Stilouri-x
Pixuri-y
20x+30y=190 lei
30x+20y=210 lei
....................... (+)
50x+50y=400 lei/50(factor comun)
x+y=8 lei=>x=8-y
20(8-y)+30y=190
160-20y+30y=190
160+10y=190
10y=190-160
10y=30
y=30/10
y=3
x+y=8
x+3=8
x=8-3
x=5
986y+789x=986*3+789*5
=2958+3945
=6903