$\"\"$

According to Means-extremes Property of proportion: If $\"\"$ , then $\"\"$ .

$\"\"$ (Cross products) $\"\"$

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

$\"\"$ (Divide each side by 2)

$\"\"$ (Cancel common terms)

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

The value of $\"\"$ .