an english teacher has been teaching a sixth grade composition class for many years he has a feeling that over the past several years the writing ability of students has changed. a national test of proficiency in composition was administered 5 years ago. the resulting distribution of scores was normally shaped had a population mean of 85 and a population standard deviation of 10.9 in order to test his feeling he gives his present class of 43 students the same proficiency test. the resulting mean is 80 and standard deviation is 8.7 the obtained value of the appropriate statistic for testing h0 is