A bridge hand consisting of 13 cards is selected at random from an ordinary deck of cards. Let H, D, C, and S be the number of hearts, diamonds, clubs, and spades in the hand. Calculate the values of the following joint probability mass functions at the specified points. a) p_{H,D,C,S}(2,1,3,7)= b) p_{H,D,S}(2,1,7)= c) p_{C,S}(3,7)= c) p_{H}(2)=