Problem:
A train covers a certain distance in 2 hours at a constant speed. If the speed is increased by 20%, it takes 1.5 hours to cover the same distance. Find the original speed of the train.

Solution:
Let's assume the original speed of the train is 'x' km/h.

Step 1: Calculating the distance:
To find the original speed, we need to calculate the distance covered by the train. We can use the formula:
Distance = Speed × Time

We know that the train covers the distance in 2 hours at the original speed. Therefore, the distance covered can be calculated as:
Distance = x km/h × 2 h
Distance = 2x km

Step 2: Calculating the new speed:
If the speed is increased by 20%, the new speed of the train will be 120% of the original speed. We can calculate the new speed as:
New Speed = Original Speed + (Original Speed × 20%)
New Speed = x + (x × 20%)
New Speed = x + 0.2x
New Speed = 1.2x km/h

Step 3: Calculating the distance with the new speed:
With the new speed, the train covers the same distance in 1.5 hours. Therefore, the distance covered can be calculated as:
Distance = New Speed × Time
Distance = 1.2x km/h × 1.5 h
Distance = 1.8x km

Step 4: Equating the distances:
Since the distance covered is the same in both cases, we can equate the distances:
2x km = 1.8x km

Step 5: Solving the equation:
Now, we can solve the equation to find the value of 'x', which represents the original speed of the train:
2x = 1.8x

Simplifying the equation:
2x - 1.8x = 0.2x
0.2x = 0

Therefore, x = 0

Conclusion:
The original speed of the train is 0 km/h. This means that the train was not moving, or there might be an error in the given information.