Please help me find the union AND intersection of each set and function.

a) A = { ( 1 , 1 + 1/n ) : n belongs to all natural numbers }

b) A = { [ 2 , x ] : x belongs to all real numbers greater than 2 }

c) A = { [ 0 , 3 ] , ( 1 , 5 ) , [ 2 , 4 ) }