G
E is incorrect because it is a whole step below F#. E# is also below F# and you are looking for the note that is a half step above. G# is too high because it is a whole step above F# because on a piano, G# to F# is a black note to a black note. This means that G is your answer because it is a half step from F#. (F# is a black note on the piano and if you press the next note, it would be a white note which is G)
