Answer:
Since this (looks) like a homework assignment/test, I'll give you a hint.
Explanation:
A function is where you have a input, that usually involves an equation that you have to replace the unknown with, to get the output.
Don't get it? Well, I didn't either.
What's great about this problem that you don't neccessarily have to know what the definition is.
A function can only output. So if you inputted the number 6, and got the output -3, you can't have another number that also had the output -3, and vice versa. This is my hint for the number 1.
Number 4 is a bit harder, but here's my hint:
Look for a pattern.