Daca a + b = 20 si b + c = 30 ,calculati 3 . a + 7 . b + 4 . c ( dau coroana la cine ma ajuta )

It is given that

a+b=20   (1)

b+c=30 (2)

We have to calculate

3 a + 4 b +7 c

Now multiplying equation(1 )by 3,we get

3 a+ 3 b=60  (3)

and Multiplying equation( 2) by 4,we get

4 b + 4 c=120  (4)

Adding expression (3) and (4),we get i.e left hand side of 3 to left hand side of 4 and right hand side of 3 to right hand side of 4.

3 a+ 3 b+ 4 b+ 4 c=60+120

Adding like terms, we get

3 a+ 7 b+ 4 c =180, Which is the required solution.

step-by-step explanation: yes

your answer would be 12