Production cost

Two products G and H are created from a joint process. G can be sold immediately after split-off. H requires further
processing into product HH before it is in a saleable condition. There are no opening inventories and no work in progress of
products G, H or HH. The following data are available for the last period:
$
Total joint production costs
450,000
Further processing costs of product H
66,000
Product
Production units
Closing inventory
G
345,000
20,000
HH
230,000
34,500
3. Using the physical unit method for apportioning joint production costs, what was the total cost of the closing inventory of
product HH for the last period?(Answer in $)

My question in why do we need to closing inventory form production unit for both products.. I didn’t get it