To find the average per day use this equation;
total number of pies ÷ total number of days = average of pies per day
78 + 96 + 104 + 40 + 77 = 395
Monday + Tuesday + Wednesday + Thursday + Friday = 5 days...
395 ÷ 5 = 79
so the average of pies sold per day is : 79 pies per day.
hope it helped :D