I have attached a problem that is similar to one that i posted earlier. I have worked this one out, but would like to know if what i have done is correct.

I came up with possible costs:

total $221.04 @ $9.21 ea

total $521.04 @ $21.71 ea

total $821.04 @ $34.21 ea

I also thought that $x21.08 would be possible too, but it turned out that these possibilities did not work. I was hoping someone could help me understand why.