Ikeep getting confused i don't understand what i keep doing wrong

so.. let's us eliminate, say "z" first, so for that, let's pick the 1s and 2nd equations there  

so, that's our first two-variables resultant

let's pick other two, and again, eliminate the same "z" variable, this time, let's use the 2nd and 3rd equations   

now, we have two two-variables equations, let's use them then
and say, we'll eliminate the "y" variable from them

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