简单的来说：就是现在的月收入X35个月
You can calculate the worth of the site multiplying the monthly income by 35 or 40x. There are a few services out there that can help u with the process of selling your website. But they charge a fee between 10-15% of the total sale of the website. I think it is worth it since they will be responsible for the transfer of the website, and responsible for you to receive your money. Motion Invest offers this service, you can take a look at their website.
https://www.blackhatworld.com/seo/what-is-the-value-of-my-website.1364384/