Răspuns :
2x+4(45-x)=140
2x+180-4x=140
-2x+180=140
-2x=180-140
-2x=40
-x=20
x=20
=> proba: 40+4(45-20)=140
40+4x25=140
40+100=140
2x+180-4x=140
-2x+180=140
-2x=180-140
-2x=40
-x=20
x=20
=> proba: 40+4(45-20)=140
40+4x25=140
40+100=140