The correct answer is 29 years.
In fact, the equation (Kepler's third law) says
[tex]P^2 = A^2[/tex]
where P is the period in years, and A is the distance of Saturn from the Sun, expressed in A.U. We know this distance, [tex]A=9.5 A.U[/tex], so we can find the period of Saturn P:
[tex]P= \sqrt{A^3}= \sqrt{(9.5 A.U.)^3}=29 years [/tex]
