Final answer:
The question contains a bearing which is a direction, not a distance measure. The straight-line distance from the lake to the waterfall is explicitly given as 12.8 km, making that the correct answer.
Step-by-step explanation:
The question asks how far away a waterfall is from a lake given the bearing and a direction, but provided information about the bearing of 242 degrees does not align with the typical method of measuring straight-line distance. A bearing indicates a direction along a compass from the north, and it does not provide distance directly. Since the question states that the waterfall is 12.8 km south of a lake, that distance is the straight-line distance between the two points. Therefore, the correct answer to the question, 'How far away is the waterfall from the lake?' is 12.8 km.