Make the span change?

Question

PHP

There is a span - uc-price
There are 2 inputs in the admin panel, 1 for euros, 1 for rubles
prices on the site in rubles.
Gently make the final price - span id="uc-price" and the input.rub field have the following formula -
uc-price = input.euro.value * kurs.value There
is a course value, I don't know much about php.
and accordingly, when changing kurs.value, all goods were recalculated

Answer 1

$euro = 1234567890; // Данные в EURO
$kurs = 2; // Ваш курс
$uc_price = $euro * $kurs;
echo "<span id='uc-price'>$uc_price</span>";
echo "<input class=rub value='$uc_price'>";
echo "<input class=euro value='$euro'>";

If something is not clear, ask

Answer 2

> span id="uc-price" and field input.rub
your question is in php and html terms, and only the word "field" somehow refers to Drupal.
study the variables in the_entity_view
hook, install the devel module
and write the command in the hook
and the code has already been hinted to you