Details Case I Case II Case III
Opening stock of finished goods ? 18000 3500
Costs of goods manufactured 104750 142500 ?
Closing stock of finished goods 24500 12000 10500
Cost of goods sold 101250 ? 152000

:p

Beginning Balance
+ Goods manufactured (once finished they go into finished goods)
= Available for Sale
- Cost of Goods Sold (which come back out of the account)
= Ending Balance

(Can also be done beginning + manufactured - ending = COGS, but the above is how they would be in the account itself, and either works for your purposes.)

Plug in what you have and try to solve for what you don't have.

How to calculat of opening stock