$\"\"$

The part is 12 and the percent is $\"\"$ .

b represent the whole.

$\"\"$ (Percent proportion)

$\"\"$

Apply cross multiplication property: $\"\"$ , when $\"\"$ .

$\"\"$

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

$\"\"$ (Divide each side by 40)

$\"\"$ (Cancel common terms)

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

The 12 is $\"\"$ of 30.