why does february have only 28 days and 29 days on leap year ??

why cant it have 31 days

and why some months only have 30 days ???

i bet only few can answer this

actually 1 year is 365 days and 6 hours but for the sake of convenience it is taken as 365 days .The remaining 6 hours add up to 24 hours or one day .After every 4 years and it is added to february month ,so that year has 366 days and february has 29 days ......................