pls help me with this question

8. Suppose a multiple regression model that explains the salaries of CEO (Y) in terms of annual sales ($, X1), return on equity (%, X2) and return on stock (%, X3) as follows: log (Y() = 4.32 + 0.280log (X1{) + 0.0174X2: + 0.00024X3: (0.32) (0.035) (0.0041) (0.00054) And n = 209, R2 = 0.283 a. Test if the variable, return on stock, has a positive effect on salary. b. By what percentage is salary to increase if the return on stock increases by 50 points? c. Would you include the variable of return on stock in the model? Why or why not