A bus crosses a bridge at a speed of 108 km/h. If the bus takes 4 hours to cross the bridge, find the length of the bridge.

Given:
Speed = 108 km/h
Time = 4 hours

Formula Used:
Distance = Speed × Time

Solution:
Distance = 108 × 4 = 432 km

So, the length of the bridge is 432 kilometers.

Thus, the correct answer is (b).