The graph of g(x) is obtained by reflecting the graph of f(x)=2|x| over the x-axis. which equation describes g(x)?

Choice C) 
g(x) = -|2x|

You get this answer by simply sticking a negative out front of the original function. In other words, g(x) = -f(x) or more technically, g(x) = -1*f(x).

The negative will flip every y coordinate from positive to negative (or vice versa)

You'll also use the idea that |2x| = 2|x|. The two can be pulled out since we can say |x*y| = |x|*|y|
So |2*x| = |2|*|x| = 2|x|