Question

why their is 28 dayes in febrary after 4 years

Answer 1

The ancient Romans were pretty pragmatic.  They didn't see a need to put a label on days that didn't need a label.  Their calendar began on the first day of March and ran through the end of December.  It was a ten month calendar (decem means ten) of 304 days.  A calendar was needed to mark schedulable events.  Wars could only be fought during acceptable weather, crops could only be planted or harvested during acceptable weather, festivals weren't much fun in bad weather.  The period between the last day of December and the first day of March was dreary.  Nothing much happened, so there wasn't a need to give it names on the calendar.

Later, according to Livy, a king named Numa decided that the calendar was really out of whack with the seasons and needed fixing.  He decided to go ahead and name those unnamed days while he was at it and added two months, January (named after the god Janus) and February (named after the festival of purification that happened a couple of weeks before the new year).

February ended up being shorter quite simply because its job was to account for the remaining days of the year after January had been added, and that number of days was less than a typical month.  Remember that the new year began on the first day of March. 

Almost seven centuries later, Julius Caesar introduced his calendar, moving the beginning of the year to January 1.