Wanting to know if there is a linear relation among heat index, air temperature (in degrees Fahrenheit), and dew point, a researched collected the following data for various days.

(a) Find the least-squares regression equation y̅ = b0 + b1x1 + b2x2, where x1 is air temperature, x2 is dew point, and y is the response variable, heat index.
(b) Draw residual plots to assess the adequacy of the model. What might you conclude based on the residual plots?