Which of the following cannot be the length of ac?

now, if you took a look at that link above, let's see.

if we take AB and BC and lie them flat, by opening up the vertex at B, the longest that'd give us is 12+14 = 26, so AC can be at most LESS than 26 units, because if it's 26, then we end up with a flat-line and lose the triangle, so 25 or less is fine for AC.

can it be 30? well, how the dickens are AB + BC going to give 30 or more than 30 really?  nope, not quite, it can't be.

11) obtuse

13)right

15) acute