Answer:
The value is [tex]v  =  2.999 *10^{8} \  m/s[/tex]
Explanation:
From the question we are told that
  The time taken to travel to the planet from earth is [tex]t = 189 \ light-years[/tex]
  The  time to be spent on the ship is  [tex]t_{s} =  12 \  years[/tex]
Generally speed can be obtained using the mathematical relation represented below
    [tex]t_s  =  2 * t *  \sqrt{1 -  \frac{v^2}{c^2 } }[/tex]
The 2 in the equation show that the trip is a round trip i.e going and coming back
=> Â Â [tex]12 = Â 2 * 189 * Â \sqrt{1 - Â \frac{v^2}{(3.0*10^{8})^2 } }[/tex]
=>   [tex]v  =  2.999 *10^{8} \  m/s[/tex]
