Answer:
2
Explanation:
this might not be the best explanation but this is how I thought of it.
f(0)=4? any number multiplied by zero equals zero so it is not the first answer.
f(2)=4? if f were to be 2, then 2*2 can equal 4 so this is a pretty good answer.
f(3)=4? there isn't a whole number you can multiply with 3 that will make 4 so this is not the answer.
f(4)=4? if f were to be 1 then this could be a possible answer.
so we know that it is either the 2nd or 4th answer. look at the table. if you look, 2 forms into 4 (because they multiplied 2 by 2). but 4 doesn't remain at 4 (because they did not multiply it by 1). so we know the answer is 2.