Hi Ms Camille

Just to confirm, you recommend that when I first pick up high notes outside my comfortable vocal range, I should use a breathy (back of the throat voice) instead of using the mix voice, right? 

Does this rule apply when I sing songs with high notes? In other words, I should only move on to mix voice once I master the high notes, right?

Hi, Kang! Yes, it's usually easiest to expand your range by first "finding" those notes in head voice/falsetto (which is naturally lighter). 

Within a song, you can feel it out on a case-by-case basis! If you can sing that high note in head voice, great. If you can add some more "mix" intensity, great! Let your voice guide (and current comfort level) guide you. 

Got it!

Thank you!

You're welcome, Kang!