The length of a side of a triangle must be less than the sum of the lengths of the other two sides and greater than the difference of the lengths of the other two sides.
12 in. + 14 in. = 26 in.
14 in. - 12 in. = 2 in.
The third side must measure more than 2 inches and less than 26 inches, but we are told that the 14-inch side is the longest side of the triangle, so the third side must measure less than 14 inches. The largest whole-number length less than 14 inches is 13 inches.
Since it must be an integer, 5 would make it up to the full length of the longest line. What you get is not quite a triangle. The way to get a triangle is to add one more to the 5 to make 6
