4. Hydraulic fracturing is often used to increase gas well production. Fracture fluid which consists of fluid and sand is pumped into the well. The following figures are (a) a scatterplot of the monthly production versus volume of fracture fluid pumped for 225 gas wells with the least squares line superimposed and (b) a residuals vs. fit plot of the same data. Both production and fluid are expressed in units of volume per foot of depth of well. The least squares regression line is, y = 106.11 + 0.1119x. 1600 1000 1400 750 1200 500 1000 250 800 Residual 0 Production (1000 ft 3/ft) 600 -250 400 -500 200 -750 -1000 2000 4000 6000 8000 200 400 600 800 1000 Fracture fluid (gal/ft) Fitted value (a) (b) a. A new well is dug and 500 gallons per foot of fracture fluid are pumped in. Based on the scatterplot, is it more likely that the production of this well will fall above or below the least-squares estimate? b. Looking at the residuals vs. fit plot, would you be concerned about violating one or more error assumption