Answer:
5<x<21
Step-by-step explanation:
when any two sides are added together they have to be greater than either side... to find the range
add the two sides together to get the upper end of the range 8+13=21
and to get the lower end of the range subtract 13-8=5
so the range is 5<x<21
the third side CAN NOT be 5 or 21, must be between them
