Kevin drove from a to b at a constant speed of 60 mph, turned immediately around, and returned at a constant speed of 80 mph. exactly 4 hours before the end of his trip, he was still approaching b, only 15 miles away from it.
what is the distance between a and b?

a. 275 mi b. 300 mi c. 320 mi d. 350 mi e. 390 mi

Let the distance between A and B = d.  

The time from A to B is d/60 and the time from B to A is d/80

The total time for the round-trip would-be: d/60 + d/80 which simplifies to 7d/240.  

Since we are given that exactly 4 hours before the end of his trip, he was still approaching B and was still traveling at 60 mph, only 15 miles away from it, we now have this:

60(7d/240 - 4) = d - 15  

Simplify:

7d/4 - 240 = d - 15  

7d - 960 = 4d - 60  

3d = 900  

Divide both sides by 3:

d = 300  

i think c. but don't trust it.

step-by-step explanation:

i am unable to solve this problem

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