b) Find in set builder notation the set of all positive integers a such that 131 = a (mod 5). c) Let (1,4), (2,3), (3,1), (4,1)} be a relations on A = {1,2,3,4}. Using Boolean matrix operations find: i R-1. R = {(1,1), (1,2), (1,3), (2,4), (3,2)} and S = {(1,3), d) Let R and S be partial order relations on a set A. Determine whether the intersection relation RnS is also a partial order on A.