Gibbs Corporation owned 20,000 shares of Oliver Corporations $5 par value common stock. These shares were purchased in 2011 for $180,000. On September 15, 2015, Gibbs declared a property dividend of one share of Oliver for every ten shares of Gibbs held by a stockholder. On that date, when the market price of Oliver was $28 per share, there were 180,000 shares of Gibbs outstanding. What NET reduction in retained earnings would result from this property dividend?

The answer is 162,000.

The solution is:

part a: (180,000/10 X 28)= 504.000

part b: (504,000 - (180,000X 18/20)) 342,000

part a- part b = 162,000

The part I'm confused about it is where did the 18/20 come from? please explain where in the problem I'm suppose to decipher that part?