The mass of the sun is 2 x 10 (30) kg, and the distance between Neptune and sun is 30 AU. What is the orbital period of Neptune in earth years

We may use the mathematical expression of Kepler's law here, which is:

T² = 4π²a³/GM

Where T is in earth years, a is astronomical units and M is solar masses. Moreover,

4π²/GM = 1, so:

T² = a³

T = √ (a³)

T = √ (30³)

T = 164.3

Neptune's time period of orbit is 164.3 earth years.