Check boxes macro

Hi all,

I have a problem trying to get a macro to work which is attached to a check box.

the background is that it is for a monthly bonus sheet. Once the site reaches a certain level of recycling then the staff may be entitled to a bonus. The manager will enter the recycling rate in a specific cell at the bottom of the spreadsheet and their is a table on a separate tab which lists the different percentages and how much bonus they get.
What I have is a tick box next to each individual (there may be reasons why certain staff dont get the bonus that month) and when the tickbox is ticked I want it to look up a percentage figure from cell B22 to work out how much bonus should be paid.

I have managed to get this to work but what I also would like that when the checkbox is unticked then the bonus figure is deleted.

Like I said, I have managed to get it to work for once the checkbox is ticked but cant get it to do the deleting bit!