Please help with 4 or 5. (You can pick one)

4. Let X1, X2, ..., Xn ~N (u, o?) where u E R and o is known. Find the minimum value of n to guarantee that a 0.95 confidence interval for / will have length no more than o/4. 5. Let X1, X2, ..., Xn ~N (u, o?) where u E R and o? > 0. Find k E R to make (0, kS2) a 1 - a confidence interval for o2