∪ = Union
∩ = Intersection
Let's find (Q u R):
[tex]\begin{gathered} Q=\mleft\lbrace L,O,N,G,I,T,U,D,E\mright\rbrace \\ R=\mleft\lbrace L,A,C,Q,U,E,R\mright\rbrace \\ so\colon \\ Q\cup R=\mleft\lbrace L,O,N,G,I,T,U,D,E,L,A,C,Q,U,E,R\mright\rbrace \end{gathered}[/tex]Now, we can find P n (Q u R):
[tex]\begin{gathered} P=\mleft\lbrace T,O,D,A,Y\mright\rbrace \\ Q\cup R=\lbrace L,O,N,G,I,T,U,D,E,L,A,C,Q,U,E,R\rbrace \\ so\colon \\ P\cap(Q\cup R)=\mleft\lbrace T,O,D,A\mright\rbrace \end{gathered}[/tex]