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. By looking at the equation of the least-squares regression line (ŷ = 85 + 16x), you can see that the correlation between amount of gas used and degree-days is: