Which cannot be X if a triangle has sides of length 7, 11, and X?

18 is also impossible, because the sum of two lenghts cannot be equal with the third, that means that the angle between sides 7 and 11 is 180, and that makes it... a line.

The answer is clearly 2- if one side is 11 and the other is 7 the 3rd side must be long enough to reach look at the possible length of the 3rd side- if the 7 is on one side of the 11 side and the x is on the other if x were 2 then even with angels of 0 degrees the 7 side would not connect with the x side
​to make a triangle the sum of the 2 smaller sides must equal more than the largest side
7+2 <11

2
The sum of lengths of two sides of a triangle cannot be less than the length of the third side. So, 2 + 7 = 9, but 9 < 11