4. An urn contains four white and six black balls. A random sample of size 4 is chosen. Let X denote the number of white balls in the sample. An additional ball is now selected from the remaining sis: balls in the urn. Let Y equal 1 if this ball is white and 0 if it is black. Find (a) E[Y|X = 2]. (b) E[X|Y = 1]. (c) Var(Y|X = 0). (d) Var(X|Y =1)