Unfortunately, you haven't shared the equations from which you're supposed to choose your answer.
But we can write our own.
When will the distance traveled by the 1st car = the distance traveled by the 2nd car?
55 miles + (55 mph)x = (60 mph)x
solve this for x: 55 miles = (60-55)x mph = 5 mph
x=11 hours
The two cars are the same distance from the starting point after 11 hours.
