my ipad mute button is stuck. how can I unmute?

There are two ways that system sounds can be muted.

Settings>General>Use Side Switch to>Mute. If you have the iPad set that way, then the switch above the volume button controls mute and unmute.

If you have the side switch set to lock screen rotation, the mute switch is a software switch in the control center. Swipe up from the bottom of the iPad to get to the Control Center and the Mute icon looks like a bell. It's in the row next to the half moon icon. If the bell is white, then system sounds are muted.

Go to settings>general>use side switch and change it from mute to lock rotation.

How do I mute the volume button on iPad 2

See Demo's post above or turn your volume all the way down till it says mute.