The problem says that the length of a train car is 50.6 feet and it is 5.8 feet less than 6 time the width. Then, you can express it as below:
L=6W-5.8
L: it is the length of the train car (L=50.6 feet).
W: it is the width of the train car.
Then, you must substitute the value of the lenght (L=50.6 feet) into the equation L=6W-5.8, and clear the width "W", to find its value, as below:
L=6W-5.8
50.6+5.8=6W
6W=56.4
W=56.4/6
W=9.4 feet
What is the width? The answer is: The widht is 9.4 feet (W=9.4 feet).