$\"\"$

The proportion is $\"\"$ .

Apply cross product property: If $\"\"$ , then $\"\"$ .

$\"\"$ (Cross products)

$\"\"$ (Multiply: $\"\"$ ) $\"\"$

Apply division property of equality: Divide each side by 21.

$\"\"$

$\"\"$ (Cancel common terms)

$\"\"$ (Divide: $\"\"$ ) $\"\"$

Apply subtraction property of equality: Subtract 9 from each side.

$\"\"$

$\"\"$ (Apply additive inverse property: $\"\"$ )

$\"\"$ (Subtract: $\"\"$ ) $\"\"$

The value of $\"\"$ .