PHP product data

Hi, i would like to change the price in the back hand depending and the number of booked room and days (dynamic pricing), which variable in the hook should i change to achieve this purpose ?

add_action(‘woocommerce_before_calculate_totals’, ‘set_custom_price’);

function set_custom_price($cart_obj) {
foreach ($cart_obj->get_cart() as $key => $value) {
if ($value[‘product_id’] == 3735) {
$value[‘data’]->set_price(9.90);
$new_price = $value[‘data’]->get_price();
}
}
}