hello!
First of all, subtract 5 from both sides:-
13-5<z+5-5
13-5<z
8<z
Since 8 is less than z, z is greater than 8:-
Hence, all the numbers greater than 8 will make this inequality true.
note:-
Hope everything is clear; if you need any explanation/clarification, kindly let me know, and I will comment and/or edit my answer :)