need some help!!

Delta, United, and American Airlines announced purchases of planes on July 18(7/18), February 12 (2/12), and October 7 (10/7), respectively. Given the above information, calculate the cumulative abnormal return (CAR) for these stocks as a group. All of the stocks have a beta of 1 and no other announcements are made. (A negative answer should be indicated by a minus sign. Leave no cells blank be certain to enter " O " wherever required. Do not round intermediate calculations and round your answers to 2 decimal places, e.g., 32.16.)