help

I think the way to go for this problem is to substitute in a few values in terms of other variables. 

I multiplied equations 1 and 2 to get ${x^2y^5z\over{xz}}=720$.

Thus, $xy^5 = 720$.

Not quite sure what to do from here, maybe you can give it a go Guest! (try substituting in variables in terms of other variables, and try plugging it into the expression)

Good luck :D!