$A$ bird is flying to and fro between two cars moving towards each other on a straight road. One car has a speed of $18 \,km/h$ while the other has a speed of $27 \,km/h$. The bird starts moving from the first car towards the second car with a speed of $36 \,km/h$ when the two cars are separated by $36 \,km$. What is the total distance covered by the bird?

(D) Given:
Speed of the first car $v_{1} = 18 \,km/h$.
Speed of the second car $v_{2} = 27 \,km/h$.
Since the cars are moving towards each other,their relative speed is $v_{rel} = v_{1} + v_{2} = 18 + 27 = 45 \,km/h$.
The initial distance between the cars is $d = 36 \,km$.
The time taken for the cars to meet is $t = \frac{d}{v_{rel}} = \frac{36}{45} = 0.8 \,h$.
The bird flies continuously at a constant speed $v_{b} = 36 \,km/h$ until the cars meet.
Therefore,the total distance covered by the bird is $D = v_{b} \times t = 36 \times 0.8 = 28.8 \,km$.