Daca a+b=300si b+c=138,afla a-c.

Răspuns :

a+b=300
b+c=138

(a+b)-(b+c)=300-138
a+b-b-c=162
a-c=162
a+b=300
b+c=138
_______-
a+b-b-c=162
a-c=162