a+b+c=198 rezulta ca a=198-b-c
b-c=123 rezulta ca b=123+c(am trecut pe c in partea cealalta si e cu semnul schimbat)
2a+b+3c=?
a+b+c=198 (inlocuim cu ce a rezultat);a=198-b-c;b=123+c
198-b-c+123+c+c=198
198-123+c-c+123+c+c=198
2c=198-198+123-123
2c=0
c=0
b=123-0
b=123
a=198-123-0
a=75
2a+b+3c=
2x75+123+3x0=150+123+0=273
proba
b-c=123
123-0=123
a+b+c=198
75+123+0=198
