(a) Given,

Length of the iron rail = 3.3 km

Converting km to m, we get,

1 km = 1000 m

Therefore, 3.3 km = 1000 x 3.3 = 3300 m

Speed of the sound in iron (V) = 5280 m s^{-1}

t = ?

5280 = 3300\over Time (t)

⇒ t = 3300\over 5280

⇒ t = 0.625 s

Therefore, **the time taken by sound to travel in iron rail = 0.625 s**

(b) Speed of sound in air = 330 m s^{-1}

Substituting the values in the above formula, we get,

330 = 3300\over Time (t)

⇒ t = 3300\over 330 = 10 s

Therefore, **the time taken by sound to travel in air = 10 s**