$\"\"$

The equation is $\"\"$ .

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

$\"\"$

Apply commutative property of addition: a + b = b + a.

$\"\"$

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

Apply addition property of equality: Add f to each side.

$\"\"$

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

Combine like terms using distributive property: $\"\"$ .

$\"\"$ $\"\"$

Apply division property of equality: Divide each side by $\"\"$ .

$\"\"$

$\"\"$ (Cancel common terms) $\"\"$

The value of $\"\"$ .