Question

a+b=3/7 si b+c=5/9 calculeaza 7a+16b+9c

Answer 1

a+b=3/7 adica 7a+7b=3

b+c=5/9 adica 9b+9c=5

adunand cele 2 relatii

7a+16b+9c=3+5=8

Answer 2

7a+7b=3

9b+9c=5

7a=3-7b

9c=5-9b

3-7b+16b+5-9b=8.

Bafta!