Since, it is given that
Now, we have to identify the addition property for the given equation.
Associative property of addition states that for any real numbers say 'a' , 'b' and 'c', a+(b+c) = (a+b)+c
So, in the given question 28+29+42
We can use associative property as
(28+29)+42 = 28+(29+42)
57+42 = 28+71
99 = 99
Hence, among the given properties, associative addition property is used.