consolidated statements of financial position bpp

On 1 January 20X0 Alpha Co purchased 90,000 ordinary $1 shares in Beta Co for $270,000. At that date Beta Co’s retained earnings amounted to $90,000 and the fair values of Beta Co’s assets at acquisition were equal to their book values. Three years later, on 31 December 20X2, the statements of financial position of the two companies were:

Alpha Co Beta Co
$ $
Sundry net assets 230,000 260,000
Shares in Beta 180,000 –
= 410,000 260,000

Share capital
Ordinary shares of $1 each 200,000 100,000
Retained earnings 210,000 160,000
= 410,000 260,000

The share capital of Beta Co has remained unchanged since 1 January 20X0. The fair value of the noncontrolling interest at acquisition was $42,000.

What amount should appear in the group’s consolidated statement of financial position at 31 December 20X2 for non-controlling interest?

Ans)
Non-controlling interest $
Fair value of NCI at acquisition 42,000
Plus NCI’s share of post-acq’n retained earnings (10% ? (160 – 90)) 7,000
= NCI at reporting date 49,000

I’ve understood the answer, sir. But what i do not understand is how we have used 10% (in the answer) when there has been no mention whatsoever of either 90% or 10%. Can you please help me out with this?