Item with 2 Parts

I have 1 Item Araldite of 3 KG which has 2 parts in it (Part A is of 2 Kg and Part B is of 1 KG) they come in a pack size of 3 KG and Rate are quoted per kg, how do i create item master with above scenario

Please check this: Anyone know why conversion factor doesn't change when save? - #2 by NCP