Question 363841
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Hi, 
Let x represent the amount of time Train B traveled.  
Then (x+7hr) represents the amount of  time train A traveled
distance = rate*time.  distance the same for both Train and Train B
60mph*(x+7hr) = 80mph*x
solving for x
60mph*x+ 60mph*7 = 80mph*x
60mph*7hr = 80mph*x -60mph*x+  
420mi = 20mph*x
21hrs = x
Takes Train B 21hrs to catch up with Train A
checking our answer
60mph*28hr = 80mph*21hr = 1680mi