Ok, so I think
X=(90-6y-7z)/5
Y=(90-5x-7z)/6
Z=(90-5x-6y)/7
I think they are related because all of the answers (a)-(c) have 90 subtracted by the following variables. Also all of the results include fractions... I don’t know for sure if this answer is right though, sorry!! I hope this helps a little though, good luck!!