Calcium is essential to tree growth because it promotes the formation of wood and maintains cell walls. In 1990, the concentration of calcium in precipitation in a certain area was 0.12 milligrams per liter (mg/L). A random sample of 10 precipitation dates in 2007 results in the following data table.

0.065 0.076 0.086 0.238 0.125
0.178 0.112 0.248 0.307 0.101
a) State the hypotheses for determining if the mean concentration of calcium precipitation has changed since 1990.