Using the regression results in column (1), is the college-high school earnings difference estimated from this regression statistically significant at the 5% level? use an appropriate statistical test to explain your answer. show your work. (b) using the regression results in column (1), is the male-female earnings difference estimated from this regression statistically significant at the 5% level? use an appropriate statistical test to explain your answer. show your work. (c) using the regression results in column (2), is age an important determinant of earnings? use an appropriate statistical test to explain your answer. show your work.