Surveying a Field

Being employed to survey a field, which I was told was an exact geometrical square, but by reason of a river which runs through part of it, I can only obtain partial measurements.  I measure 9 chains from the west corner along the south side.  Then sighting upon the northeast corner, I measure 18 chains along this line before turning and sighting back to the southeast corner which I find at an angle of 28° 30' from my path of previous sighting.  From these measurements, find the area of the field.

The Ladies' Diary, London, 1797

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