Na problem it says that x is "at most –5." what does this mean?

X would be your variable A variable is a quantity that may change within the context of a mathematical problem or experiment. Typically, we use a single letter to represent a variable. The letters x , y , and z are common generic symbols used for variables.

Witch means that X can not be more than -15 it has to be less or equal to. 

The answer would be the second choice : )