Question 720706
in ⋂ you have all *[tex \LARGE \ \ \ {x\,\in\,\mathbb{A}\,and x\,\in\,\mathbb{C}\]

A = {5, {{{highlight(10)}}}, 15, {{{highlight(20)}}} }
C = { {{{highlight(10)}}}, {{{highlight(20)}}}, 30, 40}....as you can see *[tex \LARGE \ \ \ {10\,\in\,\mathbb{A}\,and  10\,\in\,\mathbb{C}\] , and  *[tex \LARGE \ \ \ {20\,\in\,\mathbb{A}\,and  20\,\in\,\mathbb{C}\]

so,

A  ⋂  C={10,20}