The distance of Neptune and Saturn from sun are nearly 10¹³ and 10¹² meters respectively. Assuming that they move in circular orbits, their periodic times will be in the ratio : 

10√10  

Kepler’s third law T² ∝ R³ :

\(\Rightarrow \frac{T_{Neptune}}{T_{Saturn}} = [\frac{R_{Neptune}}{R_{Saturn}}]^{3/2}\)

  = \([\frac{10^{13}}{10^{12}}]^{3/2}\)

  = \(10\sqrt{10}\)