Nelson Industries manufactures a part for a type of aircraft engine that is becoming obsolete. The sales history for the last 10 years is as follows: Year Sales Year Sales
1998  945  2003 420
1999 875  2004  305
2000 760  2005  285
2001  690 2006 250
2002 545 2007 210

Required:
a. Plot sales versus time.
b. Estimate the regression model for a linear time trend of sales.
c. What is the root-mean-squared error of the linear regression estimates for these 10 years?
d. Using this model, estimate sales for year 11.