Inside of a table I place a number in and then could not delete out a total.
You have tagged Math but do you mean Writer?
If you do then pressing F2 should bring up the Formula bar. To subtract one number from another in the table click in the Formula bar after = then click on the first cell, press -, then click on the second cell and press Enter.
If this does not answer your question then please supply a sample file and explain what you want to do.
Or do you mean to delete the formula? Drag over the cell to the next cell and back to just the original cell so only the sum cell is completely highlighted, press delete.