An owner of a home in the midwest installed solar panels to reduce heating costs. after installing the solar panels, he measured the amount of natural gas used y (in cubic feet) to heat the home and outside temperature x (in degree-days, where a day's degree-days are the number of degrees its average temperature falls below 65 degrees f) over a 23-month period. he then computed the least-squares regression line for predicting y from x and found it to be: y = 85 + 16x how much, on average, does gas used increase for each additional degree-day?