Question 147112
Let t (in hour) is the time Alan and Dave can talk on their car phone.
Because they are driving from the same starting point but in opposite directons then after t hour, Alan's distance from the start is 55t.  
Meanwhile Dave only starts driving 1 hour after Alan, therefore after t hour, Dave's distance from the start is 65(t-1).
The combined distance should be equal or smaller than 250 miles.
From that, we have: 55t+65(t-1)=250 or 55t+65t-65=250 or 120t=315
Then t=315/120 or t=2 hours and (75/120)hour which is 2 hours and 37.5 minutes.