The answer is the third option, [tex]\{ x | x \leq 7\}[/tex].
They're asking you to find the union of the two sets of numbers, set [tex]A[/tex] and set [tex]B[/tex].
Set [tex]A[/tex] contains all numbers less than [tex]5[/tex].
Set [tex]B[/tex] contains all numbers less than or equal to [tex]7[/tex].
The union of both sets will include the numbers in both of the sets altogether, or [tex](A + B)[/tex]. Since any number less than [tex]5[/tex] (from set [tex]A[/tex]) is already contained in all numbers less than [tex]7[/tex] (from set [tex]B[/tex]), you can just write your final answer as set [tex]B[/tex], which is [tex]\{ x | x \leq 7\}[/tex].
Hope that makes sense!
