Answer:
G
Step-by-step explanation:
F is a step below G
(from bottom line upwards the notes are efgabcdef)
A flat (♭) is a half step lower than the note (easy to remember lower because flat is short (ya know because a flat tire has no height)
A sharp (#) is a half step higher
So if the notes go EFG, and you are adding a sharp to that middle note, the F, then a half step higher than an F# would be a G