It gets a bit easier to understand if you draw 3 triangles on a piece of paper and then "rotate" the points, meaning for one triangle you get A as the right angle, for another you get B as the right angle and for the last one you get C. You will notice that only B could be the right angle, since if it's not, then BD will be the same as AB or BC (since the triangle is a right one).
I strongly advise you try drawing what I've just described! I couldn't figure it out without that!
So you get that B is your right angle and that AB and BC are you non-hypotenuse sides. Now let's work with that.
1. is not sufficient because we know nothing about BC and have no way of finding anything out.
2. basically hands over the answer, stating that AB*BC = 24 (since they are the non-hypotenuse sides).
Hope this helps!
