why is it that the halleys comet returns after 76 years????? cant it return after 12 or 13 years????????

Earth returns to its own position after every 365 days after making one revolution around the sun. Now, the planet mercury which is the closest planet to the sun takes only 88 days to complete one revolution and the farthest planet the Neptune  takes 60,190 days. This means as the planet is away from the sun it takes longer time to revolve around. However, the shape of the orbit around the sun and the speed of the planet or comet is responsible for its return to the same place. Halley’s comet has a very large orbit around the sun and thus it returns in 76 years after completing its revolution.