Inventory Formulas

Hello everyone I just started to mess around with Excel and was wondering if it's possible to match items in 2 different columns and then subtract the QTY in 2 other columns to find a difference. I would like to match from Column A and Column C if they match then subtract from Column B and Column D. Thank you in advance for your help.

COLUMN A...........COLUMN B............COLUMN C...............COLUMN D
ITEM.....................QTY.....................ITEM...................... QTY
AAA.......................5......................DDD.............................4
BBB.......................1......................AAA.............................3
DDD......................5......................BBB.............................1
CCC.......................4......................CCC............................5
EEE........................3......................EEE............................5


NIK~