z varies directly with x^2 and inversely with y

z = k*(x^2/y)

where k is constant

When x=2 and y=4, z=3

3 = k *(2^2/4)

k(4/4) = 3

k = 3

z = (2x^2)/y

when x=4 and y=9 we have

z = (2*4^2)/9

z = (2*16)/9

z = 32/9

z = 3 5/9

z = 3,56