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 is 2.56 because per pound equals the amount
The domain is the input (x) value. Since the equation is not provided with any input limit the answer is negative infinity to infinity.
The answer is the last choice.
Step-by-step explanation:
a = 2 + 3a + 8
a = 10 + 3a
a - 3a = 10
-2a = 10
a = -5