On December 21, 2018, Evergreen Ltd. reported its financial results for the quarter ended November 30, 2018. Its net income increased to $370.5 million, or 65 cents per share, up from $175.2 million, or 31 cents per share, for the same quarter of the previous year. Its sales increased to $1.67 billion, up from $835.1 million for the previous year's quarter. These results were in line with analysts' forecasts.

On the same day, the company projected further increases for next quarter, with earnings per share expected to be in the range of 66 to 70 cents. An increase in the number of customers was also projected, due both to the company's success in penetrating new consumer markets and to favorable financial results in foreign countries.

On December 21, 2018, Evergreen's shares increased in price by $13 to $119 per share following these announcements. The return on market index on the same day is 0.0013 (RMt). Evergreen's beta is 2.43 and the risk free return is 0.0001(Rf) per day.

a. Calculate the abnormal return of Evergreen's shares for December 21, 2018 (round the results to 4 decimal places).

b. Assuming the securities market is efficient, explain why Evergreen's share price increased on December 21, 2018.