Crystal Reports sum detail field

Message

   Here is the situation:

I am running ACCPAC 5.2A over a
Pervasive.SQL V8 for workgroup. I am modifying a Crystal report 8 .rpt
file. The customer asked me to move some columns back and forth, add
some calculated formula fields, so far so good.

Now this is what
I just got stucked: The report shows transactional data of and
inventory control, you know, receivings, adjustments, issuing out of
the warehouse , etc. It looks sort of this

Fecha	        |Año/Prd.	|Número de Documento		|Tip     |Unidad	|Cantidad	|Costo Std	  Monto
09/12/2006	|2006 - 12	|SG-10085              		|Envío	|BARR.     	|-1.0000	|8,257.89 	-8,257.894

13/12/2006	|2006 - 12	|REC0000006080         		|Recibo	|535		|0.0000 	|0.00 	           362.109 
13/12/2006	|2006 - 12	|REC0000006080         		|Recibo	|535		|0.0000 	|0.00 	             1.192 
13/12/2006	|2006 - 12	|REC0000006080         		|Recibo	|BARR.     	|1.0000 	|8,070.00 	  8,070.000 

13/12/2006	|2006 - 12	|SG-10110            		|Envío	|BARR.     	|-1.0000	|8,257.89 	-8,257.894
18/12/2006	|2006 - 12	|SALDO20061218         		|Recibo	|BARR.     	|11.0000 	|8,241.95 	90,661.430 
18/12/2006	|2006 - 12	|MA-3046               		|Envío  |BARR.     	|-3.0000	|8,257.89     -24,773.683

23/12/2006	|2006 - 12	|REC0000006173         		|Recibo	|159		|0.0000 	|0.00 	      130.955 
23/12/2006	|2006 - 12	|REC0000006173         		|Recibo	|159		|0.0000 	|0.00 	      1.376 
23/12/2006	|2006 - 12	|REC0000006173         		|Recibo	|BARR.     |1.0000 	|8,070.00 	   8,070.000 
Now here's the trik I need to perform, 'Envio' means when the item goes aout of whse. 'Recibo' when goes in by a purchase.
The
problem i have is that they split the cost of the purchase in two or
three records, like these two 'Recibos' 6080 and 6173, the calculated
'Costo Std' stad cost, it is just a simple division cost / qty, but in
this case the cost is form by the three records, so It should read like
this

13/12/2006	|2006 - 12	|REC0000006080         		|Recibo	|535		|0.0000 	|0.00 	     362.109 
13/12/2006	|2006 - 12	|REC0000006080         		|Recibo	|535		|0.0000 	|0.00 	        1.192 
13/12/2006	|2006 - 12	|REC0000006080         		|Recibo	|BARR.     	|1.0000 	|8,202.331   8,070.00 //This is the important one

The column Costo Std should display the sum of the three values divided by the qty recieved

any
chance of doing this at Crystal report designer? cause i do not have
access to the program that query the data, since it is a DLL file

best regards