Answer: The answer is 100 to 140 feet.
Step-by-step explanation: Given that we are anchoring our boat and the water is 20 feet deep. We are to calculate the anchor line we should use.
General rule of calculating anchor line is given by
Multiplying the depth of the water by 5 to 7 . For example, if the water depth is 'x' feet, then we will multiply 'x' feet by 5 to 7 to get the amount of anchor line to put out.
Here, the depth of water = 20 feet.
So, the anchor line should be 5 × 20 to 7 × 20 feet, i.e., 100 to 140 feet.
Thus, the anchor line should be 100 to 140 feet.