Open Tuition notes Chap 4 -Example 1

How to derive the Fair Value of existing holding at date of obtaining cotrol ? Can someone help ?
” When Aisvydas acquired 15% of Roberta’s $400k sh.cap in 2007 for $100k, Roberta’s retained earnings were $ 200k.
2 years later Aisvydas acquired a further 60% of Roberta’s shares for $520k when the retained earnings had risen to $360k (sh.cap unchanged). The FV of the NCI – $ 200k. Calculate Goodwill and profit on deemped disposal”