3a) You are given that the mean is 60. A Chi-squared distribution with 60 degrees of freedom has a mean of 60. So just find P(X>90) using Chi-squared with df=60

3b) Use a normal distribution with mean 60 and variance 400, or standard deviation of 20. Find P(X>90) using the distribution I just described. It will also be P(Z>1.5) which is around 6.68%, look slike you got that already in your work.

4) Google Cauchy Distribution and F Distribution..... Hint the normal distribution has a connection with the cauchy. And the chi-squares have a connection with the F-distribution.