Most likely 7 (fa). But there are two schools of thought with solfegio. One is that solfegio ALWAYS starts with Do on the C. If that’s the case, then the F# becomes Fa.
The other school of thought is that Do is always the tonic of the scale. In this case G. If that’s the case, then the F# would be Ti.
So you’ll have to ask your music teacher which school of thought they abide by for the correct answer here.