I understand that you're looking to enter an equation in the amount section of a check in QuickBooks Online (QBO) to calculate the hours multiplied by the rate. Currently, this feature is unavailable in QuickBooks QBO
However, there are third-party apps and integrations that can provide this capability. I recommend exploring the QuickBooks App Store to find a solution that meets your specific needs for calculating the amount based on an equation.
From there, enter the keyword or name of the app you're looking for in the Search bar.
Once done, press the Enter key on your keyboard.
You'll be given a list of the app related to the keyword you input.
To verify the app you can use, you can check the reviews for that program.
When you find one, follow the steps in this article to install it in QBO: Install and use apps.
We have a link here where you find articles on how to manage payroll and employees in your Online account: Payroll and Workers. Then, go to the Subtopics section to see the articles you need.