If astronauts could travel at v = 0.950c, we on Earth would say it takes (4.20 / 0.950) = 4.42 years to reach Alpha Centauri, 4.20 light-years away. The astronauts disagree.
(a) How much time passes on the astronauts' clocks?
years
(b) What is the distance to Alpha Centauri as measured by the astronauts?
light-years