<PRE><B>Question 890833</B>
A = 2B
4(A+b) = 600
Substitute the value of A from the first equation into the second
4(2B+B) = 600
Divide each side by 4
2B+B = 150
Add
3B = 150
Divide each side by 3
B = 50
If the slower train is traveling 50 mph, then the faster train is traveling 100 mph.  Together they travel 150 mph.  Multiply that by four hours to get the total distance of 600 miles.
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