N₀ is set of whole numbers so, N₀^k is is cartesian product of k N_{0 sets}. Please answer this question if you know its urgent.

Let k N. A subset A N₀^k is said to be a primitive recursive set if its characteristic function x_a : N₀^k {0,1} is primitive recursive. We say that set A P RS. (a) Show that every unitary subset of N₀ is in PRS. (b) Show that every finite subset of N₀^k is in PRS.