Calculation of investment in associate (step acquis: associate to investment)

Hello Sir
Here is a question in BPP Revision Kit about disposal shareholding.
The question is:
Banana had purchased a 40% equity interest in Strawberry for $18 million a number of years ago when the fair value of the identifiable net assets was $44 million. Since acquisition, Banana had the right to appoint one of the five directors on the board of Strawberry. The investment has always been equity accounted for in the consolidated financial statements of Banana. Banana disposed of 75% of its 40% investment on 1 October 20X6 for $19 million when the fair values of the identifiable net assets of Strawberry were $50 million. At that date, Banana lost its right to appoint one director to the board. The fair value of the remaining 10% equity interest was $4.5 million at disposal but only $4 million at 30 June 20X7. Banana has recorded a loss in reserves of $14 million calculated as the difference between the price paid of $18 million and the fair value of $4 million at the reporting date. Banana has stated that they have no intention to sell their remaining shares in Strawberry and wish to classify the remaining 10% interest as fair value through other comprehensive income in accordance with IFRS 9 Financial Instruments.
(Y/E is 30/06/20X7)

The answer is at 01/10/20X7, Strawberry should have included in the consolidation at a fair value of $20.4m (18+40%*50-44)

The calculation of disposal as follows:
Proceeds 19
Fair value of retained earnings 4.5
Carrying amount of investment in associate (20.4)
Gain on disposal 3.1

My questions are:
1. How to calculate the carrying amount for the previously 40% shareholding, and the year end is 30/06/20X7, is it necessary to consider the time proportion? Because in the answer writes “at 01/10/20X7 the S should be consolidated as fair value of…” however, the parent sold part of the shareholding on 01/10/20X6.
2. In the calculation of the disposal, I can understand the proceeds and the FV of retained earnings, but why we deduct the carrying amount of investment in associate?

Thank you!