Answer:
Dolphin is 3 feet above the surface of the water.
Step-by-step explanation:
Dolphin is 30 feet below the surface of the water, then its position on the vertical number line is -30.
Thus,
[tex]-30+23-17+27\\ \\=(-30-17)+(23+27)\\ \\=-47+50\\ \\=3[/tex]
Dolphin is 3 feet above the surface of the water.