how do i answer this question

Question

Let the Universal Set, S, have 147 elements. A and B are subsets of S. Set A contains 94 elements and Set B contains 79 elements. If Sets A and B have 46 elements in common, how many elements are in A but not in B?

Answer 1

94 + 79 - 46 = 127

147-127 = 20 elements not in A or B

94-46 = 48 elements in A but not in B