Read this and answer the question. If the question is unanswerable, say "unanswerable".

The western edge of the Oklahoma panhandle is out of alignment with its Texas border. The Oklahoma/New Mexico border is actually 2.1 to 2.2 miles east of the Texas line. The border between Texas and New Mexico was set first as a result of a survey by Spain in 1819. It was then set along the 103rd Meridian. In the 1890s, when Oklahoma was formally surveyed using more accurate surveying equipment and techniques, it was discovered that the Texas line was not set along the 103rd Meridian. Surveying techniques were not as accurate in 1819, and the actual 103rd Meridian was approximately 2.2 miles to the east. It was much easier to leave the mistake as it was than for Texas to cede land to New Mexico to correct the original surveying error. The placement of the Oklahoma/New Mexico border represents the true 103rd Meridian.

When was the border between TX and NM first determined?
1819