(a) Suppose you have a function of two variables, n and k; for instance h(n,k). If you are told that h(n,k)=O(n+k), what should that mean mathematically? (b) Let f(n)=O(n) and g(n)=O(n). Let c be a positive constant. Prove or disprove that f(n)+cg(k)=O(n+k)