Answer:
 The Distance cover by both the Runners is same = 10 miles  
Step-by-step explanation:
According to question , 
The Speed of first runners (S 1) = 5 miles per hour
The speed of second runners (S 2)  = 4 miles per hour
Let The Time taken by First runner (T 1 ) = T hour
But the second runner  arrives half hour after the first runner ,
I.e The Time taken by Second runner (T 2) = ( T +  )
 )
Now from Distance = Speed × Time
Since both the runners start from same place and run along the same trail 
SO ,Both the Distance cover by both are same , D 1 = D 2
i.e Speed 1 × Time 1 = Speed 2 × Time 2
     5 mph × T            =  4 mph   ×  ( T +  )
 )
     5 T =  4 T + ( 4 ×  )
 )
 Or,  5 T - 4 T = 2
∴       T    =  2 hour  , 
Time take by first = T1 = T = 2 hour
Time take by second = T2 = T +  = (2  +
 = (2  +   )hour =
 )hour = 
Now the Distance cover = Speed × Time
               Distance   (D1)          = 5 mph  × 2 hour = 10 mile
And        Distance    (D2)         =  4 mph  ×  = 10 miles
 = 10 miles
Hence, As The Distance cover by both the Runners is same = 10 miles  Answer