I am working on a schedule where there are many different workers, and many
different shifts of different lengths are being used.  I have been trying to
create a formula that sums the total hours for each person, based on the name
in the adjacent column.  For example:

A                 B            C
4-8pm        Mark      4.00
6-8pm        Dave      2.00
8pm-11pm  Mark      3.00

My hope is that there is some conditional formatting to say if column B =
"Mark", sum the amounts adjacent to the name Mark in column C, to the output
value would be 7.00 hours.