In the well-know song "the twelve days of Christmas" a person gives his or her true love k gifts on the k-th day for each of the 12 days of Christmas and repeats each gift identically on the subsequent day. Thus the twelfth day the true love receives one gift plus two gifts plus three gifts for the third day, and so on.

a, How many gifts are received on the the twelfth day?

b, How many gifts are received over the entire 12 days?