It is tricky but the key is that the original investment of $2 million is held at fair value through profit or loss in the parent’s accounts, so this value may have changed since 1 June 2009, which it has done so.
The invetment is held in Robby’s books at $19 million per the SFP which includes the $16 million paid on 1 December 2011, so the remainder must be in relation to the initial 5% acquired and gives us a value of $3 million. The fair value of this 5% has therefore now increased from $3 million to $5 million and hence the gain of $2 million.