Find
i)$$A\cap B$$ if (i) $$A=\left \{10,11,12,13\right \}, B= \left \{12,13,14,15 \right \}$$
ii) $$A= \left \{5,9,11\right \} ,B=\varnothing$$
Find the union of the following sets.
(i) $$A=\left \{1,2,3,5,6\right \} $$ and $$B=\left \{4,5,6,7,8\right \}$$
(ii) $$X =\left \{3,4,5 \right \} $$ and $$Y =\varnothing$$