Which of the following values cannot represent the side length of a triangle? 1,2,3 3,4,5 7,7,7 9,18,10 6.5.12 2,15,14

The answer would be 6.5.12

A triangle couldn't be made if the total sum of the two shortest side is less than the longest side. In this case, the two shortest side would be 5 and 6. The longest side would be 12.
If you try to add the two lowest side, the result would be 5+6=11. That means even if you make the triangle with 179.99 degrees that the 5 and 6 look like a straight line, the longest side it can achieve is 11.

21, i'm pretty sure it's right lol