Donation days calculator issue
<p>Hey i'd like to know how can i make such calculator 
by entering the $ amount you get how many days of donation status 
as shown here 
<a href="https://www.sixth-sen.se/index.php?/donate/" rel="nofollow">https://www.sixth-sen.se/index.php?/donate/</a>
i tried several ways and codes but none of them worked </p>