Question

What property is 19 + (11 + 37 ) ?

Answer 1

An operation is associative if you can group numbers in any way without changing the answer. It doesn't matter how you combine them, the answer will always be the same.
 
$a + (b + c) = (a + b) + c \\ \\ 19+(11+37) =(19+11)+37 \\\\19+48=30+37\\\\67=67$