Follow these steps:
Estimate the point on the edge of the penalty area where your ball last crossed as it went in.
Imagine a straight line running from the hole through that estimated point and extending behind the penalty area.
Go back as far as you like and identify a spot on that line.
Measure or estimate a one club length wide relief area on either side of and behind that spot, then drop a ball in the relief area.
Your dropped ball must land in and be played from the relief area.
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