If the earth were to orbit the sun in 365.20 days how often would a leap year be necessary?

The Earth goes around the sun in about 365.25 days. It's a funny number, but we're stuck with it because that's how fast the Earth spins and how fast it orbits the sun. We deal with that fact by counting a year as being 365 days and 366 days every fourth year.

The Earth goes around the sun in about 365.25 days or 365 days and 6 hours. These six hours get added every four years to give 24 hours or 1 day.

That is why we count a year as being 365 days and 366 days every fourth year.