Carrying Amount of NCA in Consolidated SOFP

Attempted the Group Accounting Quiz via ACCA Student Virtual Learning Centre and stuck at this question, Sir, could you give some hindsight what fundamental knowledge I have missed out? ><

Rugby has a 75% subsidiary, Stafford, nd is preparing its Consolidated SOFP as at 31 Dec 20X6. The carrying amount of NCA in the 2 companies as that date as follows:-
Rugby $260000
Stafford $80000

On 1 Jan 20X6 Stafford had transferred an item of equipment to Rugby for $40000. At the date of transfer the equipment, which had cost $42000, had a carrying amount of $30000 and a remaining useful economic life of 5 years. The group accounting policy is to depreciate NCA on a straight-line basis down to no residual value. It is also group policy not to revalue NCA.

What is the carrying amount of NCA in the consolidated SOFP of Rugby as at 31 Dec 20X6?

The final answer is $260000 + $80000 – $8000. I can’t get the rationale behind the adjustment of $8000. Is anyone can breakdown the calculation and reasons ?