<?php
error_reporting(-1);
 
$dollars = 200;
$exchangeRate = 80.93;
$roubles = 10000;
 
function calkR($r, $c){
    $d = $r/$c;
    return $d;
}
 
function calkD($c, $d)
{
    $r = $d * $c;
    return $r;
}
 
 
echo "$dollars долларов можно
обменять на " . calkD($dollars, $exchangeRate) . " рублей" . "<br>";
 
echo "$roubles рублей можно
обменять на " . calkR($roubles, $exchangeRate) . " долларов";
 
$roubles = calkD($dollars, $exchangeRate);
$dollars = calkR($roubles, $exchangeRate);
 
echo "<p>" . "$dollars долларов можно обменять на $roubles рублей" . "</p>";

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