Problem. If we know how much A+B and B+C equals , then compute the following expression

A + B
=5and
B + C
=17

6A
+9B
+3C
=

Exemple !

Solution. We notice that A + C = B, so we multiply the first expression with the coefficient of A and the second expression with the coefficient of C , after which we add them up.

If A + B = 5 și B + C = 9 , we have the solution to 4A + 6B + 2C = ?

Solution. A + B = 5 then 4A + 4B = 20 , B + C = 9 and it results 2B + 2C = 18, then 4A + 4B + 2B + 2C = 20+18 , and the final result is 4A + 6B + 2C = 38.