[05holsteinn]

How do you determine angle sizes.  I believe it has something to do with lone pairs.
The professor asked us to give angle sizes for the following structures.  

N H3 - the angle between two of the hydrogens

CH3 O CH2 CH3 - the angle between the first CH3 and CH2

CH3 O H - the angle between CH3 and H

How do you know just by looking at them what the angle is?

[Mitch]

You need to know what shape the molecule makes. Check your book, it should be in there.