The head office usually issues goods to branches at

When a head office supplies goods to its branches, the usual practice, unless the question states an arrangement involving a mark-up (invoicing at selling price with a "loading" for unrealised profit), is to issue the goods at cost price, that is, the price the head office itself paid for them.

Issuing goods at cost keeps the branch's stock records straightforward: the branch simply carries the goods at what they cost the business as a whole, and any profit is only recognised when the branch actually sells the goods to outside customers. This avoids recording unearned or unrealised profit within the business's own internal transfers between head office and branch.

Prime cost and production cost describe cost concepts used in manufacturing to build up the cost of producing goods, not the value at which finished goods are transferred internally to a branch; net realisable value is the estimated selling price less costs to complete and sell, which is used for valuing stock at the lower of cost and net realisable value, not for internal goods transfers to branches.

Unless a question specifically describes a branch invoicing arrangement with an added mark-up, treat goods sent to branches as valued at cost price.