The sides of a triangle rule state that the sum of any two sides of a triangle has to be greater than the third side.
Chet using each option to determine which one is a possible value for x:
a. 5, 8, x=2



The third sum does not apply to the triangle side rule, the sum of both sides is less than the length of the third one. x=2 is not a possible side length for this triangle.
b. 5, 8, x=4



The sum of any two sides of the triangle is greater than the third one for every possible combination.
x=4 is a possible side length for this triangle.
c. 5, 8, x=14

The sum of the side lengths is not greater than the length of the third side. This side length is not valid.
d. 5, 8, x=17

The sum of the side lengths is not greater than the length of the third side. This side length is not valid.