Need help solving this problem for critical thinking

Question

Let the Universal Set, S, have 171 elements. A and B are subsets of S. Set A contains 55 elements and Set B contains 97 elements. If Sets A and B have 3 elements in common, how many elements are in A but not in B?

Answer 1

55+97-3=149

55-3 =52 in A but not in B

97-3 =94 in B but not in A

3 in both

U=171 is largely irrelevant to the problem

171-149= 22 in U but not in A or B