Complete the series.|||Question of The Day

Question:
Complete the series.



9 = 4,
21 = 9,
22 = 9,
24 = 10,
8 = 5,
7 = 5,
99 = 10,
100 = 7,
16 = ?, 17 =?

Answer:   
16 = 7 and 17 = 9 [The number of letters in the spelling of 16 (sixteen) is 7 and that of 17 (seventeen) is 9]