Question 990320
.
You are given 

<pre>
X + Y     = 26, 

    Y + Z = 23, 

X     + Z = 37.
</pre>

Add all three equations. &nbsp;You will have


2*(X + Y + Z) = 26 + 23 + 37 = 86.


Hence,


X + Y + Z = {{{86/2}}} = 43.