Alright, all the equations are correct, but only two will figure out how many 1/2 servings she can make.
Your answers are A and D.
A adds the ingredients together for the total, 16, and D shows how many servings you can make. If you're making 1/2 pound servings, then the equation
16 / 1/2
would turn into
16/1 * 2/1
and that would turn into
16*2
which equals
=32