Can you fill the blank spaces; 19=8, 6=3, 70=7, 8=5, 4=4, 60=5, 15=7, 16=? 17=?

All of the numbers are being put with how many letters are in the word.  

For example 19=8: N I N E T E E N & 6=3: S I X, etc.

So if we have 16=? and 17=?...  

16 would be 7 because there are 7 letters in the word:

S I X T E E N.  

17 would be 9 because there are 9 letters in the spelling of the word:  

S E V E N T E E N.

I hope this helped.~

16=? : 7

17=? : 9

Hope this helped

1) 2/5

2) zero=0/1

3) zero=0/2

4) -4/5

5) undefined=3/0