1) 5 + ( 2 + 7) = (5 + 2) + 7
It is the associative property of the addition.
This property states that when adding 3 numbers, the grouping or association of the numbers does not change the result.
2) The second expression is unreabable
3) h + 0 = h
It is the identity property.
This property states that 0 is the identity element of the addition and any number added to it is equal to the same number.
AS you know, 5 + 0 = 5, 1234 + 0 = 1234; 0 + 2548 = 2548.