$192
If we multiply the 24 drawing by $12 for each drawing we get $288, the total she made at the art fair. By multiplying this total by 1/3, we get $96 which is the amount she spent on books. If we subtract the $96 spent from the $288 she made, we get $192, the amount she put into her savings account.
24 * $12 = $288
$288 * 1/3 = $96
$288 - $96 = $192