You have the following inequality:
z/4 ≤ 12
To solve the previous inequality you proceed as follow:
z/4 ≤ 12 multiply both sides by 4
z ≤ 48
Hence, the solution is z ≤ 48
when you want to graph a solution of the form "z lower or equal than", you draw a black point, that means the solution are all number lower than 48, including 48.
