Two trains A and B of length 400 m each are moving on two parallel tracks with a uniform speed of `72 km h^(-1)` in the same direction, with A ahead of B. The driver of B decides to overtake A and accelerates by `1 ms^(-2)`. If after 50s, the guard of B just brushed past the driver of A, what was the original distance between them ?

Explanation

To solve the problem, we need to find the original distance \( x \) between the two trains A and B before train B starts to accelerate.

### Step-by-Step Solution:

1. **Convert the speed of the trains from km/h to m/s:**
\[ \text{Speed} = 72 \text{ km/h} = \frac{72 \times 1000}{3600} = 20 \text{ m/s} \]
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