The distance of a star from the Sun, as measured in the rest frame of the Sun and star, is 5.3 light-years. Consider a spaceship that departs the solar system at a speed c bound for the star, when the two clocks: one at the Sun and the other at the spaceship, are synchronized at t = 0. Calculate the time of arrival of the spaceship in the rest frame of the Sun: 

(a) as measured by the Sun clock. 

(b) as measured by the spaceship clock.

In order to prolong one's life, observer A starts a journey leaving observer B behind. If A moves a round trip at the steady rate of 5 x 102 m/s for 102 s according to the clock of B. How much less have A aged than B?