Explanation: \(\text{Solve: } v = 5 \, \text{kmh}^{-1} = \frac{5000}{3600} \, \text{ms}^{-1} = 1.39 \, \text{ms}^{-1}\) \(t = \frac{d}{v \sin\theta} \implies \sin\theta = \frac{d}{vt} \implies \theta = \sin^{-1}\left(\frac{d}{vt}\right)\) \(\theta = \sin^{-1}\left(\frac{500}{1.39 \times 720}\right) \, \text{[সবকিছু S.I. এককে নেওয়া হয়েছে]}\) \(\theta = 30^\circ\) \(\text{Ans. (A)}\) \(\text{ব্যাখ্যা: }\) \(\text{AC পথে রওনা হলে, } t = \frac{d}{v \sin\alpha}\) \(\text{AD পথে রওনা হলে, } t = \frac{d}{v} \, \text{[}\sin90^\circ = 1\text{]}\) \(\text{AE পথে রওনা হলে, } t = \frac{d}{v \sin\theta}\)