Question 1012997
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In the figure plane E is parallel to plane F, AB is perpendicular to F and AG is the perpendicular bisector of CD. If m∠C-AB-D = 30, what is m∠BDC?
Image: https://gyazo.com/d2c76b9ec1433620e10a45ca1461bd86 
Last tutor was absolutely useless, he told told me I'm wrong, please help me with this, take a look at the gyazo for clarification.
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In your writing, please explain what is this: m∠C-AB-D = 30.


Usually, an angle is denoted by one letter (symbol) or by three letters (symbols).


This term m∠C-AB-D is unusual and requires additional explanations.
Would you please provide them?


I think that the previous tutor pointed you the same thing.