My Professor said that the Fractional-Share rights rights outstanding, common , is 300 potential shares. Using the information below how did he calculate that number

12/31/2020

Retained earnings [ 12,000 shares x 10% $10].....................Debit 12,000

Common stock dividend distributed [at par $6]................................................Credit 7,200

Additional paid-in capital................................................................................................Credit 4,800

03/01/2021

Common stock dividend distributable.............................Debit 7,200

Common stock [75% of the dividend}............................................................ Credit 5,400

Fractional-share Rights Outstanding [25%].................................................Credit 1,800

04/01/2021

Fractional Share rights outstanding................................ Debit 1,800

Common stock (1/2)...................................................................................................Credit 900

Additional paid=in capital (1/2)..............................................................................Credit 900