C is one step above B

The answer is C. Since B is one half step up from B flat, and C is one half step up from B, and two halves make a whole :)

B flat.

I picture it on the piano, one key is one semi-tone or half a tone. Two of these makes one whole tone, or one whole step. One half step down from C would be the note B, another half step would then go to B flat. That is one whole step.

C Natural is a whole step above B flat. If you look at a piano, a half step above B Flat is B Natural, and one more half step above that is C Natural. So it's a whole step from B Flat to C Natural.

I see only one step here. This is a difference of squares.

The formula for that is a^2 - b^2 = (a + b)(a - b)

Step one. Plug it in.

(1 - 625^2)(1 + 625^2)