The eliminate command in the corrected worksheet I attached to my last reply returns a list of two sets. The first set contains an equation for the eliminated variable. The second set contains the expression that results from using the first equation. This expression is the left side of an equation whose right-side is an unwritten zero.
In my usage of the command, I appended , open and close square brackets. This causes the list brackets from the equate command to be dropped, so that the return is now just a sequence of two sets.
I then wanted to solve for z in the second "equation" returned by "eliminate." To access this expression, I used q, the second set in the returned seqence. But this referenced the second set, so to get rid of the set braces around the desired expression, I used q, in other words, the first thing inside the second member of the sequence q.
The isolate command is like a weak solve command that returns an equation whose left-hand side is the variable solved for.
These are operations that become familiar to users of 1D math input, the linear form advocated by so many of the respondants to this forum. This is the kind of thing I had to teach my students back when Maple had only the worksheet interface. They didn't like having to learn a computer language just to implement their math. That's why I see so much utility and value in the Typeset (2D math) input mode. It eliminates the need to teach students the minutiae of Maple manipulations that are only in service of Maple itself, not of the math you're trying to get Maple to do.
I could have done all the steps in the Corrected Worksheet in a syntax-free mode, but that requires explanatory text to describe what I would have clicked on, etc. I chose not to do that because it is indeed faster to use 1D input. But given your confusion over the syntax used, I have to ask "Was it really faster for the learner to have used what was faster for me?"