If a ordered pair is a solution of the system of inequalities, then the ordered pair must lie on the shaded area of the solution of the system of inequalities
The regression line equation is , the value of the slope is shown as constant 16 and it's a positive constant, hence the correlation between the amount of gas used and degree of the days is a POSITIVE correlation.
It may be useful because sometimes ur estimations and when u get your answer half of the time it's very close to it or a number less or a number higher