In this task, you are given two sets, and you need to count the number of elements at the intersection of two given sets.  A Set is shown by two curly braces and comma-separated numbers inside, like {1, 2, 3}. The intersection of two given sets is the largest set which contains all the elements that are common to both sets. To find the intersection of two given sets, A and B is a set consisting of all the elements common to both A and B.
Q: Set1: '{9, 4, 15}', Set2: '{1, 2, 3, 4, 9, 10, 13, 15, 16}'. How many elements are there in the intersection of Set1 and Set2 ?
A: 
3