Python requires function implementation, file

. Programming ： Create a file a.txt,a Each row in contains the following data ：
30, 23, 45
32, 65, 47
33, 45, 67
Generate the file B,B Each line in is A The average of the values corresponding to each row in ( Keep two decimal places ). As above data , be b is ：
32.67
48.00
48.33
Function is required to implement .