Properties:
1) a+ b = b+a Commutative
2) (a + b) + c = a + (b+c) Associative
3) a(b+c) = ab + ac Distributive
Here we are given
11 + (19 + 6) = (11 +___) + 6
The number 19 is missing on the right.
So we have
11 + (19 + 6) = (11 +19) + 6
This looks like Property 2 above.
Hence it is associative property.
