Sample surveys conducted in a large county in a certain year and again 20 years later showed that originally the average height of 400 ten-year-old boys was 53.8 inches with a standard deviation of 2.4 inches, whereas 20 years later the average height of 500 ten-year-old boys was 54.5 inches with a standard deviation of 2.5 inches. Use the four steps of testing hypothesis at 0.05 level of significance to test the null hypothesis Musub1-Musub2=-0.5 against the altenative hypothesis Musub1-Musub2<-0.5.