In the attachment I have my work scanned and I must find the formula for the upper sum and then take the limit.

My work will show what I have learned in class and I really don't recognize any of the options given to be one of the formulas.

However, by process of elimination I would guess E) would be the correct formula but even then I do not understand this completely.

My main point of confusion is normally I would write it as f(Xk) and not f(k), do these mean the same thing?