Answer:
f(6) = 23
Explanation:
-7, -1, 5, 11 is a combination in which there is a pattern of 6 adding on.
f(6) means that what would the 6th # be in terms of using this pattern.
Since we have 4 numbers already you would add 12 because 2 * 6 = 12
thus f(6) = 23