Marla has 3 secret code cards. The first shows a 37. The second card has the first box blanked out and the second box is a 2. The two code cards together equal the third card which is 59. Why is the missing number?

37 + 10A + B = 59

10A + B = 22
10A + 2 = 22
10A = 20 making A = 2 or
37 + 22 = 59