Question 868531
1.{{{A+B=40}}}
2.{{{B+C=34}}}
3.{{{A+C=42}}}
Subtract eq. 1 from eq. 2,
{{{A+C-A-B=42-40}}}
4.{{{C-B=2}}}
Now add eq. 2 and eq. 4,
{{{C-B+B+C=34+2}}}
{{{2C=36}}}
{{{C=18}}}
Then,
{{{18-B=2}}}
{{{B=16}}}
and finally,
{{{A+16=40}}}
{{{A=24}}}