A highway connecting cities A and B is 600 miles long. At 7:00 AM, a delivery truck
leaves city A and takes the highway, heading toward city B at 50 mph. One hour later
(8:00 AM), a second delivery truck leaves city B and takes the highway, heading toward
city A at 60 mph. Determine which one of the following equations would correctly use x
to solve for the number of hours the second delivery truck has been driving when the two
of them meet on the highway.