\( 1 \leftarrow \quad \) Use the associative law of multiplication to write \[ (21 \mathrm{x}) \mathrm{y} \]

To use the associative law of multiplication, we can rearrange the expression \( (21 \mathrm{x}) \mathrm{y} \) without changing its value. The associative law states that the way in which factors are grouped in multiplication does not affect the product. Thus, we can rewrite \( (21 \mathrm{x}) \mathrm{y} \) as: \[ 21 \mathrm{x} \mathrm{y} \] This expression shows that we are multiplying \( 21 \), \( \mathrm{x} \), and \( \mathrm{y} \) together, and the grouping of the factors is not important.