- Neptune is a kind of planet in the solar system
- Planets in the solar system orbit the sun
- Hence, neptune orbits the sun in the solar system

- Neptune orbits the sun in the solar system
- Furthest / farthest means greatest / most / highest in distance
- Neptune is the planet that is furthest to the sun in the solar system
- So, the distance between neptune and the sun it orbits is the greatest in the solar system

- The distance between neptune and the sun it orbits is the greatest in the solar system
- As the distance of a planet from the star it orbits increases , the length of a planetary year on that planet will increase
- Hence, neptune has the longest solar year / planetary year in the solar system

So, neptune has the longest solar year / planetary year in the solar system
Question: Which planet has the longest planetary year?
Context: - Furthest / farthest means greatest / most / highest in distance 
- As the distance of a planet from the star it orbits increases , the length of a planetary year on that planet will increase 
- Neptune is a kind of planet in the solar system 
- Planets in the solar system orbit the sun 
- Neptune is the planet that is furthest to the sun in the solar system