Directions: Solve the following problem and select the correct option.

An express train A measuring 250 meters in length crosses a 550-meter long bridge in 40 seconds. If train B has a length that is twice that of train A and travels at a speed of 126 km/h, calculate the time (in seconds) required for train B to completely cross the same bridge.

The correct answer is 30.

Step 1: Calculate the length of Train B and the total distance to cross the bridge.

Given that the length of Train A is 250 meters and Train B has a length that is twice that of Train A:

$\text{Length of Train B}=2\times 250=500\text{meters}$

The length of the bridge is 550 meters.

The total distance Train B must cover to completely cross the bridge is the sum of its own length and the length of the bridge:

$\text{Total Distance}=500+550=1050\text{meters}$

Step 2: Convert the speed of Train B from km/h to m/s.

The speed of Train B is 126 km/h.

To convert speed from km/h to m/s, multiply by 5/18:

$\text{Speed of Train B}=126\times \frac{5}{18}=35\text{m/s}$

Step 3: Calculate the time required for Train B to cross the bridge.

Using the time formula:

$\text{Time}=\frac{\text{Total Distance}}{\text{Speed}}$

$\text{Time}=\frac{1050}{35}=30\text{seconds}$

Therefore, Train B requires 30 seconds to completely cross the bridge.