A spaceship travels at constant velocity from Earth to a point 710 ly (light years) away as measured in Earth's rest frame. The ship's speed relative to Earth is 0.9999c. A passenger is 20 years old when departing from Earth.

a) How long does it take the spaceship to reach the other planet according to people on Earth?
b) How old is the passenger when the ship reaches its destination, as measured by the ship's clock?
c) If the spaceship sends a radio signal back to Earth as soon as it reaches its destination, in what year, by Earth's calendar, does the signal reach Earth? The spaceship left Earth in the year 2000.

I'm not sure how the relationship with lightyears works I think I understand the equation but not how to use it with light years for units.
I believe we would use the equation
Δt= Δto/√(1-V2/C2)

Δt= Dialated time (in motion with respect to events)

Δto= Proper time (observer at rest relative to events)

V=Speed (m/s)

C=Speed of light in a vacuum (m/s)

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