Struggling on this problem retaining to sets

Question

Let the Universal Set, S, have 100 elements. A and B are subsets of S. Set A contains 45 elements and Set B contains 61 elements. If Sets A and B have 20 elements in common, how many elements are in neither A nor B?

Answer 1

sets A U B have 45+61 -20 = 106-20 = 86 elements in either A or B

elements that are not in A or B are 100 - 86 = 14