Flat Rate Shipping with multiple Carriers and Multiple Products

[camwoodbats]

I am trying to implement flat rate shipping such that - 

Product A = $15,95 (no additional charge for additional quantities) / configured as Carrier 1

Product B = $25.95 (no additional charge for additional quantities) / configured as Carrier 2

Product C = FREE Shipping  / configured as Carrier 3

 

If Product B is in cart with product A then, 

Shipping = $25.95,

else if 

Product Product B is in cart with product C then, 

Shipping = Free, 

else if  

Product C is in cart with product A, 

Shipping = Free, 

Else if

Product A is in cart shipping = $15,95 (no additional charge for additional quantities)

else if 

Product B is in cart shipping= $25.95 (no additional charge for additional quantities)

else if 

Product C = FREE Shipping

End if 

 

Can someone point me to a module or the file that I need to rewrite to make this happen in 1.6?

 

 

Thanks