Departmental accounts

Please refer to IPCC Study Material on Advanced Accounting. Chapter : Departmental Accounts Illustration No. 2 ( Complex Ltd. )

In the Working Notes on Unrealised Profit On Closing Stock of Dept. B, the Transfer amount received from Dept. A is

Rs. 18,000. How is this figure of Rs. 18,000 arrived at ? Can somebody please explain ?

Thanks and regards.