$350 * 30/100 = $ 105 which is down payment.
$350 - $105 = $245 which is left.
But he will pay $24.50 * 12 = $294 instead.
$294 - $245 = $49
He will pay $49 more.
He paid $105 as down payment and will pay $294 more with 12 months.
Total will be $105 + $294 = $399