Yes, I can help you with that! The symbol you are looking for is called the "x-bar" symbol, which represents the mean or average of a set of values. Here's how you can insert it into your Excel spreadsheet:

1. Click on the cell where you want to insert the x-bar symbol.
2. Go to the "Insert" tab in the Excel ribbon.
3. Click on the "Symbol" button in the "Symbols" section.
4. In the "Symbol" dialog box, select "Arial Unicode MS" as the font.
5. Scroll down until you find the x-bar symbol (it should be near the bottom of the list).
6. Click on the x-bar symbol to select it, then click the "Insert" button.
7. The x-bar symbol should now appear in the selected cell.

Alternatively, you can also use the keyboard shortcut to insert the x-bar symbol. Here's how:

1. Click on the cell where you want to insert the x-bar symbol.
2. Press the "Alt" key and hold it down.
3. While holding down the "Alt" key, type on the numeric keypad (make sure "Num Lock" is on).
4. Release the "Alt" key.
5. The x-bar symbol should now appear in the selected cell.