What function do i use?

eg.
DATE PAYMENT CODE
01/03/2010 J96
01/03/2010 B24
02/03/2010 C25
04/03/2010 J96
04/03/2010 U96
04/03/2010 J96

im trying to count how many times the letter J in payment code is used in a
specific date.... eg how many J codes was used on 04/03/2010?

Please help.