Question

a+b = 12, b+c=8 cat e b-c =? .........1 x a + b + c =? .........3 x a+b+2 x c = ? .........................7 x a + 3 x b + 4 x c = ?

Answer 1

A+b=12
A=7
b=5 =) 7+5=12

b+c=8
b=5
c=3 =) 5+3=8

b-c=?
5-3=2

1xa+b+c=?
1x7+5+3=
=7+5+3
=12+3
=15

3xa+b+2xc=?
3x7+5+2x3=
=21+5+6
=26+6
=32

7xa+3xb+4xc=?
7x7+3x5+4x3=
=49+15+12
=64+12
=76

Succes!