Calculating a price per item with markup for two fields

Hi everyone,
Im having a real drama gettin my spreadsheet to do what i want it to, if you can help that would be so awesome

Basically my spreadsheet look like this:

C D E F G H
itemA priceA itemB priceB %increase SalePrice


I have two items, they can be sold seperatley or together.
If I have an ItemA AND an ItemB this formula works to calculate the base sale price (per item befor i calculate a total)

=(((C3/C3*D3)*G3/100)+D3)+(((E3/E3*F3)*G3/100)+F3)

however if there is only one of the two items being sold, and one of these columns =0, my formula doesnt work
Can anyone Help me decipher this conundrum and offer me some help?

Thank you so much, CHAMPION!