Help please if your kind enough, which one should I choose?

There is a rule:

One input(x-value) can only have one output(y-value) in order to be a function.

If one input has more than one output, it is not a function.

(This doesn't apply to outputs, meaning that one output can have more than one input and still be a function.)

4. This is a function because each input has only one output.

Your answer is the 1st option

the monthly balance will be $75,000

what is the rest of the question? ?