BPP revision kit N7 Harrington 2.5 6/05

Hi everybody. i am stuck on BPP revision kit Harrington Q adjustment i) included in sales revenue is $300 000 being the sale proceeds of an item of plant that was sold in January 2005. the plant had originally cost $900 000 and had been depreciated by $630 000 at the date of its sale. other than recording the proceeds in sales and cash no other accounting entries for disposal of the plant have been made. All plant is depreciated at 25% per annum on the reduscing balance.
i only took 300000 proceed from revenue
what book says
to take 300000 from revenue and $30 000 disposal profit add to the cost of sales. why!???????
i feel sick of this paper! this is the second time i failed F7!!!!
many