By the triangle inequality theorem we know that
b - a < c < a+b
where a and b are the given sides; c is the unknown side
In this case,
a = 12
b = 13
c = n
So,
b-a < n < b+a
13-12 < n < 13+12
1 < n < 25
So n is both greater than 1 and also less than 25
Broken up, this means n > 1 and n < 25
So it looks like the only answer is choice A. Choices C and D seem to have typos in them? Something seems off about them.
