How do I calculate the following:

In column A I have the names of a number of suppliers, B contains the
budgeted cost of work, C contains invoiced value, D contains formula
displaying "over "or "under" budget. This information transfers to a summary
table for the month showing supplier and total value of work. i want to add
a column to the summary table showing the number of jobs that went over
budget for each supplier. I have been trying to use the countif function but
I get an error every time? Also is it possible to show the number of jobs
over budget for each supplier as a percentage?
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Josie