Answer:
8
I made a couple of assumptions so you might want to make sure I made the right assumptions.
I assumed you meant square root of z; not source of z.
I also assumed you meant x=2 not x=z.
Explanation:
y varies directly with means y=k times something where k is a constant.
Inversely means to divide by whatever it says it varies inversely with.
So we have:

We are given y=4 and x=2 and z=4, which means:




So the constant is k which means the equation for any (x,y,z) is:

We want to know y when x=6 and y=9:



