Question

a+b+c=? a+b=42, a+c=54, c+b=40

Answer 1

a+c=54
a+b =42
se scad cele doua relatii
a+c-a-b=54-42
c-b =12

c+b =40
c-b=12
adunam cele doua relatii
c+b+c-b= 40+12
2c=52
c=26
c+b=40 ⇒ b=40-c ⇒ b= 40-26 
b=14
a+b= 42 ⇒ a=42-b ⇒a=42-14 ⇒ a= 28
a+b+c=  28+14+26= 68

Answer 2

a + b + a + c + c + b = 42 + 54 + 40

2a + 2b + 2c = 136

2(a + b + c) = 136

a + b + c = 68