Two trains leave the same station at the same time, but are headed in opposite directions. one train travels at 70 mph and the other train travels at 80 mph. how much times passes until the trains are 600 mi apart? enter your answer in the box.

Thank you for posting your question here. Based on the above problem, the number time passes until the trains are 600 mi apart is 555 miles. Below is the solution. 

90t + 95t = 90(t-3)+95(t-3)+d 
90t + 95t = 90t+95t-270-285+d 
0 = -555 + d 
d = 555 miles