[tex]=3h\ x\ \frac{60 \min}{1h }\ x\ \frac{60\ sec}{1\ min}[/tex]
[tex]=10800\ sec[/tex]
Set up your equation so that your units cancel until you get to the unit you want. Hours and hours would cancel, and min and min would cancel, leaving you with sec which is the unit you want.
Remember: they can only cancel if one is on top and the other is on the bottom.
