Question

x+x=40
2y+2y+2y=30
x+z=23
x+y+z=?

Answer 1

x= 20 pois
x+x=40
2x=40
x= 40/2

y=5 pois
2y+2y+2y=30
6y=30
y= 30/6

z=3 pois x=20 entao 
20+z=23
z=23-20
z=3

x=20     y=5      z=3
x+y+z=28