Puzzle

1. Complete the series. 9 = 4, 21 = 9, 22 = 9, 24 = 10, 8 = 5, 7 = 5, 99 = 10, 100 = 7, 16 = ?, 17 = ?

2. In a year, some months have 30 days, while some have 31. Guess, which month has 28 days?