Not sure about c and d

(6 pt) Let X be a random variable with a cumulative distribution function of le) = 3375/x"3 + 1, when x >= 15, and F{x) = 0, when x 30) = ? (1 pt) b. Write out the probability density function of X. [1 pt] c. What is the standard deviation of X? {For this question, you do NOT need to calculate out the final number. Just write out the formula with corresponding numbers plugged in. l (2 pt] d. Let Y be another random variable such that Y = 1/(15X)"3. Calculate the expected value of Y. (Again, no need to calculate out the final number, but you have to carry out the integration.) (2 pt)