Question: Substitution techniques

Having read the above I decided to try it on a substitution problem I had last year on a set of equations. Work sheet containe an example. I successifuly applied algsubs to the problem. It can be slow and their is no easy way I see to know when the substitution is complete. so what I did go round the loop 2, 3, 4, 5 times. Crude!

Decided to try "side relations" with simplify here but it comes out with a totally different answer (not correct).

Could somebody explain why?

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