Answer:
Q1)  Time taking by particle to travel the 40 km wrt. earth =  sec.
 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.
 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
, 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,
 improper length,  proper length (distance measured wrt. rest frame) = 40 km
proper length (distance measured wrt. rest frame) = 40 km 
      
      
       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)
 improper time (wrt. earth frame time)  ,
 ,   proper time (wrt. particle frame).
 proper time (wrt. particle frame).
  
  
Thus, the time taking by particle to travel from where it is created to the surface of the earth  .
.