Rounds 15-18

It's the final stretch! Make it through these rounds, and you're done with most of Billy:

Round 15:
[7 sc, dec] x 4
Round 16:
[dec, 2 sc] x 8
Round 17:
[sc, dec] x 8
Round 18:
dec x 8

Stuff as needed, and you're done! You might be looking at your piece and wondering – now wait a minute. Why is there a giant gaping hole in the middle of my piece? 

Never fear, there's a tutorial here: