An endocrinologist is interested in the effects of depression on the thyroid. It is believed that healthy subjects have a mean thyroxin (a hormone related to thyroid function) level of 7.0 micrograms/100 ml and a standard deviation of 1.6 micrograms/100 ml. The endocrinologist wants to assess whether the mean thyroxin level is different for those with depression. She gathers a sample of 35 subjects with depression and obtains a sample mean of 7.82 micrograms/100 ml. What are the null and alternative hypotheses for this study?