Given:
The statements and reasons to solve an equation.
To find:
The missing reason.
Solution:
If a, b and c are three real number, then
Associative property of addition :
Commutative property of addition :
Multiplicative property of equality :
Distributive property of multiplication over addition :
In the given step, is written as
.
It means, only parenthesis are changed, which is possible by Associative property of addition.
So, the missing reason is Associative property of addition.
Therefore, the correct option is A.