The function f(x) = c is a CONSTANT function, represented by a horizontal line of the form y = c.
Therefore, when we use the verification for Even function: f(x) = f(-x), we get that it is TRUE (since the value of the function is always "c" no matter what value of x we pick):
f(x) = c
f(-x) = c
Then, this is an even function, and therefore has symmetry around the vertical y-axis.
The line of symmetry is the y-axis itself.
The function is NOT ODD, since it doesn't verify the condition for odd function:
f(x) = - f(-x)
because:
f(x) = c
- f(-x) = - c
and c doesn't equal "-c"