[SoLiDUS]

Here's an Algebra problem I've created:

[code:53b64]

X X Y 40

Z Y Z 50

X Y Z ?

35 50 50
[/code:53b64]

I want you to solve it WITHOUT resorting to an individual variable solution,
that is to say I don't want you solving X, then Y and Z: there's an alternate
way of finding the value of the line. Simple numerical answers will not count:
I want the details of your solution.