(Actually, now that I look at it, I'm not sure this answers your question at all. You've just been given a liner equation, and an uncertainty... Usually linear equations are accompanied by a correlation coefficient, not an uncertainty. )
I was asking some questions along this line some months ago
The main thing that ought to be distinguished is systematic errors and random errors. You might not have any "random error" in your x-values, because you are measuring the same x-value in the same way, and getting the same result.
However, there may be a systematic error in your measurement of your x-value.
A quick google search gave me this article which gives some more detail:
I'm not entirely certain how to account for possible systematic errors... You can really only account for systematic errors you KNOW are present.