A fire engine is located at point A on a straight east-west road. A warehouse that has caught fire is located 4 miles east of A and 1 mile north of the road. The engine can travel at 48 mi/h on the road and 20 mi/h across the open field. It will leave the road at a point that is x miles east of A (0≤x≤4) and then drive straight to the warehouse. What is the least possible travel time?
a) 9.2 minutes
b) 7.7 minutes
c) 6.5 minutes
d) 12.4 minutes