Mac Keyboard Short-cut for Math

Hi, I was wondering if there is a keyboard shortcut on Mac computers where you can be put a bar above a letter? For instance, x with a line on top ("x bar"). An application is writing the mean of a variable (x bar) in a mathematical equation. Thank you!

I found one with a bar under it but none on top. Go to System Preferences/Keyboard and click 'Show Keyboard & Character Viewers in menu bar' box.
Click the little box in the menu bar, maybe you can find one. If you find one, drag it to your text.

For a one time use, just try a copy & paste.

Thanks everyone for your help! The copy and paste solution works great.