Your lead writing brush has lead in it. What kind of writing instrument has lead in it? How about a pencil?

This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own. Just be careful because the ひつ gets rendaku'd to ぴつ. In case you need help with this rendaku reading, here's a mnemonic:

You know how some people put a pencil behind their ear? Well, you keep yours between your pits (ぴつ). Why? So your friends will stop mooching pencils off you in class. No one wants a gross sweaty pencil you've been keeping between your pits.