Unfortunately, arsenic occurs naturally in some ground watert. A mean arsenic level of u = 8.0 parts per billion (ppb) is considered safe for agricultural use. A well in Texas is used to water cotton crops. This well is tested on a regular basis for arsenic. A random sample of 31 tests gave a sample mean of x = 7.2 ppb arsenic, with s = 2.1 ppb. Does this information indicate that the mean level of arsenic in this well is less than 8 ppb? Use a = 0.05. (a) What is the level of significance? State the null and alternate hypotheses. O Ho: M 8 ppb; Hi: M = 8 ppb O Ho: M = 8 ppb; H1: H > 8 ppb O Ho: M = 8 ppb; H1: u