$\"\"$

The part is 12 and the whole is 400. You need to find the percent.

Let n represent the percent.

Part = percent $\"\"$ whole

12 = n $\"\"$ 400 (Substitute part = 12 and whole = 400) $\"\"$

$\"\"$ (Divide each side by 400)

$\"\"$ (Cancel common terms)

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

$\"\"$ (Multiply with 100 and add percent sign)

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

12 is 3 $\"\"$ of 400.