Remember that the domain is the set of all the possible x-values.
Similarly, the range is the set of all the possible y-values.
This way, we'll have that:
[tex]\begin{gathered} Dom(T)=\mleft\lbrace-1,2,7\mright\rbrace \\ Ran(T)=\mleft\lbrace-8,7\mright\rbrace \end{gathered}[/tex]