Basic Groups- Associates

Hi Sir Slight confusion over this question. The P group (comprising P and it's subsidiaries) acquired 30% of the equity share capital of A on 1 October 20X6, enabling P to exercise significant influence over the operating and financial policies of A. A made a profit for the year ended 30 June 20X7 of $600,000. Profits are deemed to accrue evenly over the year. Between 1 October 20X6 and the reporting date, A sold goods to P for $600,000 at a margin of 20%. P still held one quarter of these goods in inventory at 30 June 20X7. At 30 June 20X7, an impairment review was carried out and it was determined that the investment in A was impaired by $20,000. Calculate the amount that would appear in the consolidated statement of profit or loss of the P group for the year ended 30 June 20X7 in respect of the investment in A. My workings: Profit= 600,000 * 9/12= 450,000 Deduct: Depreciation= 0 Impairment=20,000 Pup= (1/4*600,000)*20%=30,000 total =400,000 Parents share= 30% of 400,000 = 120,000 however the answer is 106,000 and in the workings the parents share was calculated before impairment was deducted. e.g Profit= 600,000 * 9/12= 450,000 Deduct: Depreciation= 0 Pup= (1/4*600,000)*20%=30,000 Parents share= 30% of (450,000 -30,000) = 126,000 less impairment =20,000 = 106,000 my question is why is impairment deducted after we take the 30% parents share? and not before thanks