Anorthbound bus and a southbound bus are at a bus stop at the same

In New York I Milly Rock, hide it in my sock
Running from an opp, and I shoot at opp (what)
And I'm on the block (what, what, what)
And I'm on the block (what)
In New York I Milly Rock (hello?) hide it in my sock (what)
Hide it in my sock (what) selling that rerock (what, what, what, what, what)

Answer 20 centimeters15+8=2323-3=20so the answer is 20 centimeters

The answer is part a: use