I am having problems understanding how to find the transitive closure of a Relation. Here is the problem:

Given U = {1, 2, 3, a, b} and the relation R on U is given by R = {(2,3), (3,2), (1,a)}

How does one find the transitive closure of R? I have found both the symmetric and reflexive closure, but don't know how to solve for the transitive.