Suppose you have 2 columns of data. Data gets added to the columns
frequently.

A B
xyz 4
abc 3
jkl 5
xyz 2
abc 1
def 4
abc 3

I need to calculate the total number in column B for the last 2
entries. Thus, if looking for "abc", the answer would be 4 (3+1),
since the abc got a 3 the last entry and 1 for the previous entry.
Using the same formula for xyz would return 6 (2 +4).

Any ideas on how I can accomplish this?