A random sample of 85 sixth graders has a mean (x-bar) score of 265 with a standard deviation, = 55, on a history assessment

A random sample of 85 sixth graders has a mean (x-bar) score of 265 with a standard deviation, σ = 55, on a history assessment test. The test result prompts a school administrator to state that the mean score for the sixth graders on the test is more than 260. α = 5%.

What is the value of the test statistic (z-value)?