How large of a sample should one select to be 86% confident that the sampling error is 10 or less. Assume that the population standard deviation is 250.

I am struggling to find the z value based on 86% confidence and the examples on here aren't helping clarify things for me. The lookup table has confidence levels for 60%, 80%, 90%, 95%, 97.5%, and 99% and I'm struggling to understand how to calculate the z value for any confidence level. Please clarify.

Thank you