Answer = 82

Formula is (3rd Number * 10 + 1st number) - 2ndNumber

1,5,8 = (8 * 10 + 1) - 5 = 81 - 5 = 76

2,7,3 = (3 * 10 + 2) - 7 = 32 - 7 = 25

3,4,9 = (9 * 10 + 3) - 4 = 93 - 4 = 89

4,5,7 = (7 * 10 + 4) - 5 = 74 - 5 = 69

therefore

5,3,8 = (8 * 10 + 5) - 3 = 85 - 3 = 82