The value attributable to the VCO’s is 40% x 46144 = 18458.
If they had not increased the equity ownership they would only have had 20% and so the value attributable would have been 20% x 46144 = 9229, and so the increase is the difference between the two, which is 9229.
Given that 20% is half of 40% then the value of 20% can be also calculated (as the examiner has done) by taking 50% x 18458 = 9229.