Answer:
Q1) Time taking by particle to travel the 40 km wrt. earth =
sec.
Q2) The distance traveled by particle where the particle created to surface of earth wrt. particle's frame = 3.84 km.
Q3) The time taking by particle to travel from where it is created to the surface of the earth =
sec.
Explanation:
Given :
Speed of particle wrt. earth 
Distance between where particle is created and earth surface = 40 km
we know that,
⇒ 
Where
,
, we know speed of light 
∴ 


∴ Thus, time taking by particle to travel the 40 km wrt. earth 
According to the lorentz transformation,
⇒ 
Where
improper length,
proper length (distance measured wrt. rest frame) = 40 km


km
∴ Thus, the distance traveled by particle where the particle created to surface of earth wrt. particle's frame = 3.84 km.
According to the time dilation,

Where
improper time (wrt. earth frame time)
,
proper time (wrt. particle frame).


Thus, the time taking by particle to travel from where it is created to the surface of the earth
.