A super train travels 1,500 miles in 12.5 hours. How many miles does it travel in one hour?

I assume you've heard of the phrase "mph" or "miles per hour". Per is normally associated with the division symbol in mathematics.

You have your miles (1,500) and you have your hours (12.5)

Divide 1500 by 12.5.

1,500 : 12.5 = 120

The super train travels 120 miles per hour.

Let's treat the speed in one hour as a variable.

We can say that 1500=12.5x

Divide by 12.5

1500/12.5 = x

x = 120

120 mph is your answer.