instruction:
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.
question:
Set1: '{9, 3, 6, 7}', Set2: '{3, 4, 9, 10, 11, 15, 16, 17, 18}'. How many elements are there in the intersection of Set1 and Set2 ?
answer:
2


question:
Set1: '{1, 10, 6}', Set2: '{3, 4, 6, 7, 8, 20}'. How many elements are there in the intersection of Set1 and Set2 ?
answer:
1


question:
Set1: '{9, 11, 13, 15, 19}', Set2: '{4, 11, 12, 13, 15, 16, 17, 20}'. How many elements are there in the intersection of Set1 and Set2 ?
answer:

3