Janice is considering buying a new home. She wants to estimate the monthly utilities (heating and air conditioning). She figures that the utilities are dependent on the size (square footage) of the home. She collects data on 10 homes in the neighborhood and finds a linear model to give the relationship between the size of the home and the monthly utilities. The equation of the line is ŷ = –8.1 + 1.91x, where ŷ is the mean monthly cost in utilities and x is the square footage of the home. The residual plot is shown. Based on the residual plot, is the linear model appropriate?