setup googles invisible recaptcha on an html form -- $15

I will not pay more than $15.00 for this. Currently the website on form submit posts the form data to mysql and redirects the user to a URL depending on if they answered correctly. I need help setting up Googles reCAPTCHA without breaking anything. It's one single HTML page. IF they fail the capture they're sent to $first_url and if they pass the form they're sent to $second_url (this two variables already exists and the function is already created to send a user to one or the other depending on their form answers compared to an array)