CHECK BOX HELP PLEASE.

My sheet contains 80 rows. (80 competitors). Their results are posted, one
row to a competitor. Starting on row 7
I have a check box (default €“ unchecked) in cell K7. Its purpose is to
indicate if that persons times should qualify for the event. This check box
will be in Col k on every row. There are three timers. The three times are
averaged to give €œThe Time€�. If they run over their time, this checkbox
should be clicked and the previously entered times in C7,E7,E8 should be
replaced with NIL. I can record a macro to do this on that line, but I want
to use a relative function so that I can copy it down the page to make the
same thing happens on every row (if needed). I have nearly been there but
everytime I get close, I seem to come up with something not quite right. Any
help please much appreciated.