since an even function is defined as a function with the following rule. f(-x) = f(x) for all x in the domain of f(x). It would be odd if f(-x) = -f(x) for all x in the domain of f(x). If f(-x) ≠ -f(x), than it is neither. these are all known as the parity of a function.
you can apply these rules to all of given functions like this. (-x-1) ≠ -(x-1) so it is neither. 8(-x) = -(8x) so it would be odd. 2(-x)-(-x) = -(2x-x) so it is odd as well. This would make f(x) = 7 the only option, as there are no x variables in the equation so 7 = 7.
