Given information:
- The average speed of a train is five times the average speed of a car.
- The difference in time taken by the train and the car to cover a distance of 1260 km is 168 hours.

To find:
The time taken by the train to cover the same distance.

Let's solve the problem step by step:

Step 1: Understanding the relationship between speed, distance, and time.

We know that speed is defined as the distance covered per unit time. The formula to calculate speed is:
Speed = Distance / Time

Step 2: Understanding the given information and setting up equations.

Let's assume the average speed of the car is 'x' km/hr.
According to the given information, the average speed of the train is five times the average speed of the car, which means the average speed of the train is 5x km/hr.

The time taken by the car to cover a distance of 1260 km can be calculated using the formula:
Time taken by car = Distance / Speed of car

Similarly, the time taken by the train to cover the same distance can be calculated using the formula:
Time taken by train = Distance / Speed of train

The difference in time taken by the train and the car is given as 168 hours. Therefore, we can set up the equation:
Time taken by train - Time taken by car = 168

Step 3: Solving the equations.

Substituting the values in the equations, we get:
1260 / (5x) - 1260 / x = 168

To simplify the equation, we can multiply through by 5x:
5 * (1260 / (5x)) - 5 * (1260 / x) = 5 * 168
2520 / x - 6300 / x = 840

Combining the terms with the same denominator, we get:
(2520 - 6300) / x = 840
-3780 / x = 840

To solve for 'x', we can cross-multiply:
-3780 = 840x

Dividing both sides by 840, we get:
x = -3780 / 840
x = -4.5

Since the speed cannot be negative, we discard the negative solution.

Step 4: Calculating the time taken by the train.

The average speed of the car is 4.5 km/hr, and the average speed of the train is 5 times that, i.e., 4.5 * 5 = 22.5 km/hr.

Using the formula for time, we can calculate the time taken by the train:
Time taken by train = Distance / Speed of train
Time taken by train = 1260 / 22.5
Time taken by train = 56 hours

Therefore, the time taken by the train to cover the same distance is 56 hours, which is equal to 42.

Let the average speed of the car = x km per hour