Answer: 21 more miles
Step-by-step explanation: 
Gabriel ran 
 
Logan ran 

now we change to an improper fraction 
Gabriel 

Logan 

now we find their LCM 
LCM of 5 and 4 is 20
we convert the fraction into a number in order to know the miles taken by the two boys
Gabriel
×20 = 5÷20
 =4
 6×4=24miles
Logan
×20=4÷20
 =5
 9×5=45miles
how long Logan took more than Gabriel
45-24=21miles more