It is called a constant.
Remember a "variable" means that the value of that term can change depending on the value of the "x" or "y". Since (in this case), -6 does not have a variable attached, it will not change, it will remain CONSTANT.
C is the correct answer. The method of sampling can be considered both biased & unbiased
How many hours do you drive though...
Uh yeah I agree. Mhmm. Absolutely.