Modify This Code To Add-up Numbers In COL-D

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I managed to do the combine the row if column B matches. However column D(quantity, number value), i want the quantity to add-up if column B matches. Any idea how do I modify the code below to do that?

for example:
TDG-**002 Tuna Cheese Pizza Bar (KG) KG 30
TDG-**002 Tuna Cheese Pizza Bar (MG) MG 30
TDG-**002 Tuna Cheese Pizza Bar (KG) KG 30

will combine to become
TDG-**002 Tuna Cheese Pizza Bar (KG) KG 60