Question 375367
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Hi,
z varies directly with x and inversely with the square of y
Let k represent the constant of proportionality
If I am understanding your question properly
{{{z = k(x/y^2)}}}
When x=5 and y=9, z=900  
900 = k(5/81)
(81/5)900 = k
14580 = k
equation of variation
{{{z = 14580(x/y^2)}}}