To find the time it takes to travel 900 miles at a speed of 30 miles per hour, you can use the formula:
\[ \text{time} = \frac{\text{distance}}{\text{speed}} \]
Here, the distance is 900 miles and the speed is 30 miles per hour, so the time can be calculated as:
\[ \text{time} = \frac{900 \text{ miles}}{30 \text{ miles per hour}} = 30 \text{ hours} \]
Now, to find a rate that can be set equal to \(\frac{30 \text{ miles}}{1 \text{ hour}}\) in order to express this scenario, we can set it equal to \(\frac{900 \text{ miles}}{\text{question mark hours}}\).
So, the correct rate to set is:
\[ \frac{900 \text{ miles}}{\text{question mark hours}} \]
Thus, the answer is:
\(\frac{900 \text{ miles}}{\text{question mark hours}}\)