Question

Given set M:= (-3,2) U [4,6] U {10} in the reals.
Prove that (-3,2) U (4,6) is the largest open set contained in M and [-3,2] U [4,6] U {10} is the samlled closed set which contains M.
I understand this idea and could explain it in a paragraph but im struggling to write the mathematical proof. Help would be appreciated.