$($i$)$ Calculate

$(2$ marks$)$

The three$-$day return earned by your firm for the period from the day before the announcement day to the day after the announcement date

The two$-$day return earned by your firm for the period from the day of the announcement to the day after the announcement date.

What is the purpose of calculate both them instead of calculate $3$ days return only $?$

Does it mean i have to calculate interim stock prices and final stock prices for both firms $?$

How to calculate $3$ days return, $2$ days return and excess return $?$