A kite is moving horizontally at a height of `151.5 m`. If the speed of the kite is `10 m/s`, how fast is the string being let out, when the kite is 250 m away from the boy who is flying the kite? The height of the boy is 1.5 m. (A) `8` m/s (B) `12 ` m/s (C) `16` m/s (D) `19` m/s