To find out how long it takes to drive 90 miles at the same rate, first, we need to determine the driving speed.

1. Calculate the speed:
   Speed = Distance / Time
   Speed = 240 miles / 4 hours = 60 miles per hour.

2. Calculate the time to drive 90 miles:
   Time = Distance / Speed
   Time = 90 miles / 60 miles per hour = 1.5 hours.

So, it would take 1.5 hours to drive 90 miles at the same rate.

Would you like more details on this calculation or do you have any questions? Here are some related questions to consider:

1. How would the time change if the speed increased to 70 miles per hour?
2. What is the time taken for different distances at the same speed?
3. How do you convert hours into minutes for time calculations?
4. What is the formula for calculating average speed?
5. Can you provide examples of other scenarios with different distances and times?

Tip: Always ensure to convert units appropriately when calculating speeds and times!