Relation between z-scores and percentiles; Chebyshev’s theorem)

Suppose you have a sample of data for a particular variable. Within this sample, there is a particular observation, say X Within the sample, what is the maximum possible percentile that  that has a z-score of –2.85. could represent? In other words: Suppose you had access to this sample data, and that you then could calculate which percentile X represents within the data. What is the maximum possible percentile that X could be?