A common process produces several joint products. After the common process has been completed each product requires further specific, and directly attributable, expenditure in order to 'finish off' the product and put it in a saleable condition. Specify the conditions under which it is rational to undertake:
(i) The common process, and
(ii) The final 'finishing off' of each of the products which are the output from the common process.
Illustrate your answer with a single numerical example.