Answer:
Kepler's third law:
P^2 = K R^3 the period squared is proportional to the cube of the radius
Ps^2 = K Rs^3
Pe^2 = K Re^3
Ps^2 / Pe^2 = Rs^3 / Re^3 dividing equations
Ps = (Rs / Re)^3/2 * Pe
Ps = (1.4E9 / 1.5E8)3/2 * 1 yr
Ps = 28.5 yrs
(Actual = 10759 da / 365.25 da = 29.5)