Hey guys, I don't understand how to simplify these problems, since they are different from what i've seen before.

-|4.2| I don't even know what to do with this.

|12 - 16| I thought it was -4, but my friend told me it was actually 4.

|-7/6| Again I don't know how to do this

Also just another question is -√2 a positive number?

Your help would be appreciated!