Need help with a Statistics question about A multiple regression model

A multiple regression model Y=B0+B1X1+B2X2+B3X3+E was fitted to some data with dependent variable Y (sales volume) and independent variable X1 ( marketing cost in ”00”), X2 ( number of employees) and X3 ( length of TV advert in minutes). The computer output ( R software) is as given below.

                            Estimated Std. Error t value Pr(>ITI)

(INTERCEPT)  128.6390     37.2618   3.4523    0.0014

x1                        10.0207      0.3834   26. 78862  0.0000

x2                          8.7718       1.92856   6.82357   0.0000

(i) is this model valid? give reasons

(ii) What is the meaning of dfl and dfl2 and where do these values come from?

(iii) intercept the coeficient of X3