He worked it out with a pencil.
Works it out with a pencil.
Because they always work problems out with a pencil.
Ten. (Shame this one doesn't work too well for reddit - the funniest part of this joke is the third punchline enjoying people struggle to understand what the hell you're talking about.)
I don't know, it's not my side work.
A brick-layer.
In the end, both are lucky to produce a stool.
