Question 731564
In a triangle, the length of one side is less than the sum of the lengths of the other two sides.
So,
{{{x<4+8}}} --> {{{x<12}}} to begin with.
Also,
{{{8<x+4}}} --> {{{8-4<x}}} --> {{{4<x}}}
Considering those two inequalities together tells us that
{{{highlight(4<x<12)}}} so {{{x}}} is between 4 and 12.
 
NOTE:
Why is it that in a triangle, the length of one side is less than the sum of the lengths of the other two sides?
That is because the "one side" is the "straight line" connecting two vertices, and its length is the distance between those two points measured along the straight line.
The sum of the lengths of the other two sides is the distance between the same two vertices when you go the long way, making a stop over at the third vertex.