To find out how many miles the A train travels per hour, you can use the formula:
\[ \text{Speed} = \frac{\text{Distance}}{\text{Time}} \]
In this case, the distance is 300 miles and the time is 8 hours.
\[ \text{Speed} = \frac{300 \text{ miles}}{8 \text{ hours}} = 37.5 \text{ miles per hour} \]
So the answer is 37.5 miles.