3. let a = (-1,3), b =(3, 3), c = { in € n), and d = {-1,0,1,2}. (a) [2 marks) which of the listed sets a, b, c, d are subsets of a? (b) (1 mark] calculate an d. (c) (2 marks] find a - b. express your answer as a union of two intervals. (d) [1 mark] are the sets b and c disjoint? circle: yes no