Bianca's first step involves regrouping the terms on the left side of the equation. This step can be justified using the Associative Property of Addition.
The Associative Property states that the way in which numbers are grouped when adding does not affect the sum. In this case, Bianca is changing the grouping of the numbers \(4\) and \(4 + x\) to \((4 + 4) + x\), which illustrates that the property allows for the rearrangement of terms in an additive expression without changing the result.