C# Excel search and combine

Question

Hello,
I have an excel file I generate through a C# program. The file is a combination of data from two database tables organized by Product, Part Number, and Month. I am trying to find an elegant way to combine fields by searching by Part Number and Month and adding the necessary fields together. The below orange highlighted fields are what I need to find and the yellow is what needs to be added together. Essentially take these two sections and combine them into one. 
If someone could point me in a good direction that would be awesome!
 

PRODUCT	COMMODITY	REPORT_DATE	FRUPN	YYYYMM	MONTHYR	FRUCNT	DIF	REPL	TARGET
FRU_FF_ALL_USD	DD	201309	5048998	201210	12-Oct	4076	125684	2	525000
FRU_FF_ALL_USD	DD	201309	5048998	201211	12-Nov	4034	120365	0	525000
FRU_FF_ALL_USD	DD	201309	5048998	201212	12-Dec	4022	124232	2	525000
FRU_FF_ALL_USD	DD	201309	5048998	201301	13-Jan	4018	124381	1	525000
FRU_FF_ALL_USD	DD	201309	5048998	201302	13-Feb	4026	112327	0	525000
FRU_FF_ALL_USD	DD	201309	5048998	201303	13-Mar	4023	124603	4	525000
FRU_FF_ALL_USD	DD	201309	5048998	201304	13-Apr	4022	120471	2	525000
FRU_FF_ALL_USD	DD	201309	5048998	201305	13-May	4013	124166	0	525000
FRU_FF_ALL_USD	DD	201309	5048998	201306	13-Jun	3979	118924	2	525000
FRU_FF_ALL_USD	DD	201309	5048998	201307	13-Jul	3937	121816	3	525000
FRU_FF_ALL_USD	DD	201309	5048998	201308	13-Aug	3928	121572	2	525000
FRU_FF_ALL_USD	DD	201309	5048998	201309	13-Sep	3918	117142	3	525000
PRODUCT	COMMODITY	REPORT_DATE	FRUPN	YYYYMM	MONTHYR	FRUCNT	DIF	REPL	TARGET
FRU_FF_ALL_ESD	DD	201309	5048998	201210	12-Oct	16456	507419	8	525000
FRU_FF_ALL_ESD	DD	201309	5048998	201211	12-Nov	16426	492407	12	525000
FRU_FF_ALL_ESD	DD	201309	5048998	201212	12-Dec	16499	508916	7	525000
FRU_FF_ALL_ESD	DD	201309	5048998	201301	13-Jan	16612	510790	145	525000
FRU_FF_ALL_ESD	DD	201309	5048998	201302	13-Feb	16501	461255	12	525000
FRU_FF_ALL_ESD	DD	201309	5048998	201303	13-Mar	16577	510622	13	525000
FRU_FF_ALL_ESD	DD	201309	5048998	201304	13-Apr	16715	498952	11	525000
FRU_FF_ALL_ESD	DD	201309	5048998	201305	13-May	16730	516832	25	525000
FRU_FF_ALL_ESD	DD	201309	5048998	201306	13-Jun	16790	500242	44	525000
FRU_FF_ALL_ESD	DD	201309	5048998	201307	13-Jul	16720	515942	18	525000
FRU_FF_ALL_ESD	DD	201309	5048998	201308	13-Aug	16849	517897	13	525000
FRU_FF_ALL_ESD	DD	201309	5048998	201309	13-Sep	16855	502933	13	525000