After 200 gallons used the freight train has traveled 25 miles. This means that we need to divide both sides by 200 to get a singular gallon's worth of miles traveled. 200/200 is 1, and 25/200 is 0.125.
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<u><em>IF</em></u> it were how many gallons per mile, you would divide both answers by 25 resulting in <u>8 gallons per mile.</u>