Question 908937
Let runner A be the faster runner


Runner A: speed of r+2


Runner B: speed of r


Let's say we start the clock/stopwatch at the moment runner A passes runner B. Put another way, we can think of it as they are both starting at the same time at a starting line in a race. At the starting point, t = 0


Both runners are running for the same length of time (t) according to the time modeling described above. Let t be time in hours.


Distance runner A has ran: D = (r+2)*t = r*t + 2*t


Distance runner B has ran: D = r*t = r*t


-------------------------------------------------------


Subtract those distances: (Runner A) - (Runner B) = (rt + 2t) - (rt) = 2t


This difference is 2t


We want to know when the difference is 0.75 miles, so 


2t = 0.75


t = 0.75/2


t = 0.375


It will take 0.375 hours


0.375 hours = 0.375*60 = 22.5 minutes


22.5 minutes = 22 minutes, 30 seconds


-------------------------------------------------------


There are multiple ways to answer, but I'd go with <font color="red">22 minutes, 30 seconds</font>


So it takes <font color="red">22 minutes, 30 seconds</font> for runner A to be 0.75 miles ahead of runner B.