Freight Allocation

Hello everyone, Thanks for looking at my thread. I need some help on the attached file. I have invoice number on column A. There are a lot of different items on each invoice. Some of them has freight charge, some not. All different items has different cost. I need to come up with a formula (column E) that allocate the freight cost (column D) to each item based on the item cost (column B).

I hope I explain it well enough.

Thanks,

Jackson