Keep getting syntax error (comma) in query question

[manzo]

I'm trying to to nested iif statements. I copied it down just like my professor did and it's not working for me. Here is the formula.
" Depth_Level: IIf([Depth]<15="surface",IIf([Depth]<40="shallow",IIf([Depth]<100="medium","deep"))) "


To the left of this field would be the label Depth with a bunch of numbers.

[June7]

You might want to look at the professor's example again. It should be:
IIf([Depth]<15,"surface",IIf([Depth]<40,"shallow",IIf([Depth]<100,"medium","deep")))

Where you have = signs should be commas.