This 3rd exercise is the most awkward until you get used to it. The scale spans one and a half octaves and 5 strings and as you move up the fret board and across the strings the fingering patterns change as the scale ascends and descends with your vocals.
This will give your voice, fingers and brain a good work out while you are trying to follow the notes up the scale.
Check out my Vocal Warm Up Techniques page for details on how to hum and perform lip rolls and tongue trills.
Here is the video for the tab above.