The given sets are
[tex]\begin{gathered} A=\mleft\lbrace s,t,a,r\mright\rbrace \\ B=\mleft\lbrace m,a,t,h\mright\rbrace \end{gathered}[/tex]The given question is
[tex]A\cap B[/tex]This means we need to list the comment elements in both sets
Since the common letters are t and a, then
[tex]A\cap B=\mleft\lbrace a,t\mright\rbrace[/tex]