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# A SONAR (sound navigation and ranging) uses ultrasonic waves to detect and locate objects under water. In a submarine equipped with a SONAR the time delay between generation of a probe wave and the reception of its echo after reflection from an enemy submarine is found to be 77.0 s. What is the distance of the enemy submarine? (Speed of sound in water = $1450 m\: s^{-1}$).

$\begin {array} {1 1} (A)\;55 \: km & \quad (B)\;50\: km \\ (C)\;55.8\: km & \quad (D)\;50.8\: km \end {array}$