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I also agree with the solution and arrived at the answer b. The convertible preferred shares are anti-dilutive because (450,000+250,000)/(100,000+250,000)=2 which is the same as the EPS of (450,000-250,000)/100,000=2.
Therefore to calculate the dilutive EPS=(450,000-250,000)/(100,000+60,000)=1.25
(100,000×10)/25=40,000 so that means the net dilutive impact of the stock option is 100,000-40,000 (that the company was able to reduce by buying back share in the open market due the the funds received.)
Hope that helps.