PHP add and remove Vat from Price

function vat_add($price, $vat)
{
    $nett = $price;
    $gross = $nett * ($vat / 100) + $nett;
    return $gross;
}

function vat_remove($price, $vat)
{
    $gross = $price;
    $nett = $gross-($gross * ($vat / 100));
    return $nett;
}