Given:
In July:
Number of days he has done the homework = 6
Number of days he has not done the homework = 4
In August:
Number of days he has done the homework = 16
Number of days he has not done the homework = 7
In September:
Number of days he has done the homework = 14
Number of days he has not done the homework = 4
In October:
Number of days he has done the homework = 14
Number of days he has not done the homework = 8
In November:
Number of days he has done the homework = 16
Number of days he has not done the homework = 4
In December:
Number of days he has done the homework = 5
Number of days he has not done the homework = 10
To find the months in which the difference between the number of days with homework and with no homework greater than 6.
Now,
In July,
The difference between the number of days with homework and with no homework = 6-4 = 2
In August,
The difference between the number of days with homework and with no homework = 16-7 = 9
In September,
The difference between the number of days with homework and with no homework = 14-4 = 10
In October,
The difference between the number of days with homework and with no homework = 14-8 = 6
In November,
The difference between the number of days with homework and with no homework = 16-4 = 12
In December,
The difference between the number of days with homework and with no homework = 10-5 = 5
Hence,
In 3 months the difference between the number of days with homework and with no homework greater than 6 and these are: August, September, November.