When Kim was working in her Microsoft® Excel® spreadsheet, she accidentally placed her book on the spacebar and erased the contents of cell B12. What tool can she use to fix her error?

The undo tool.

Explanation:

Microsoft Excel is a spreadsheet application developed by Microsoft, it is used for analysing data. It's worksheets are made up of columns and rows or fields and records.

There are different ways of entering data to a cell. Click on the cell and type the data, copy and paste to the target cell, double-click on the cell to correct data and click on a cell and press the spacebar key to clear the data.

Excel records the action of event, so when a mistake is made like deleting a crucial cell data value, the undo tool is used to recover the data, since it holds records of events. The redo tool is the reverse of the undo tool.