I believe I wrote my answer on another thread, where you hadn't shown your table; they've been combined now.

In post #4 the ceiling function is mentioned. Do you know about that?

We need to know what you are learning. If you only know about basic linear functions, then you would have to assume that x is a whole number. The problem would be very simple. If you need to write an expression that works for any positive number, then you will need something like the ceiling function, and we need to know what you have learned about.

So please tell us about the course you are taking and recent topics covered.