Need help on these, need explanation too please.

1.Which of the following is equavlant to (2z^3)/(8z^(n-2))

a. 1/4z^1-n

b. z^5-n

c. 1/4z^(5-n)

2.Find the range of negative squareroot (36-x^2)

so far I gotten (x+6)=-6 and (x-3)=6 so would it be y:y -6<y<6?

3. Find all solutions for sin^2=3cos^2

4. Suppose -2x+y=4 and 3x-5y=-6 whats y/x=