The sum of any 2 sides of a triangle must be bigger than the length of the third side.
Given 2 sides we can make 3 inequality's to solve:
Let X = the length of the third side.
#1) 14 + 4 > x
18 > x
#2) 14 + X > 4
x > 4-14 = -10 ( This doesn't work because we can't have a side length that is a negative number)
#3) 4 + X > 14
x >14-4 = 10
So using #1 and #3 X has to be greater than 10 and less than 18
The length of the third side is 11.