A binary operation on a set R is called associative if it satisfies the associative law: \((x \times y)\times z=x \times (y \times z)\) for all \(\displaystyle{x},{y},{z}∈{R}\)

We know that the usual operator addition \((+)\), subtraction \((-)\) and multiplication \((\times)\) all are binary operator and all these operator satisfies the associative property.

In order words, if you are adding or multiplying it goes not matter where you put the parenthesis.

Thus using the associative property we get \((-6+3)+1=-6+(3+1)\)