Trying to convert PHP apps to sidebar widgets

A client hired me to convert his HTML/CSS web site into a WordPress site. Everything went smoothly, except for two PHP calculators in his sidebar that I don’t know how to make function in WordPress. You can see them at https://otrloads.com — it’s the Mileage calculator and weather checker in the right sidebar.

I used the hack found at https://www.emanueleferonato.com/2011/04/11/executing-php-inside-a-wordpress-widget-without-any-plugin/ to get the text widget to execute PHP, but I think the problem is that I’m not sure how to connect the forms to the actual PHP files that make them work. I’m not really all that knowledgeable about PHP and I’m in a little over my head with these apps. Any guidance y’all can give me will be muchly appreciated.

Thanks,
Jean