Answer:
The answer is V = 0.9*C
Explanation:
from the relativity formula we have to:
Δt = γ * Δto
Clearing γ:
γ = Δt/Δto
Replacing values:
γ = 2070 s/900 s = 2.3
γ = 1/((1-(V/C)^2)^1/2)
1/((1-(V/C)^2)^1/2) = 2.3
1/(1-(V/C)^2) = 2.3^2
1/(1-(V/C)^2) = 5.29
Clearing V:
V = C * ((1 - (1/5.29))^1/2) = 0.9*C