Please help set up a simple equation

https://www.loom.com/share/dc739621c4c143569eb65bd447537f5c

The above is a video walkthrough of what we need. 

Thank you for sharing the video and explained clearly how you would like your form to work.

You would have to use the user defined amount in your Payment type to be able to add additional computation in your payment and use conditions.

To do this :

1) Set your payment type to user defined amount

2) Add a single choice field as your donation options and assign values to the fields.

Guide:https://www.jotform.com/help/301-How-to-Assign-Calculation-Value

3) Add a short text entry or a calculation widget so that you can store your calculation

4) Add your option for the user to select if they will pay through credit card with fee

5) use conditions to calculate the total based on the selection

A)Condition when user selects No to card fees

B)Condition when user selects Yes

6) Assign the total calculation to your payment field

Guide:https://www.jotform.com/help/275-How-to-Pass-a-Calculation-to-a-Payment-Field

Sample Form:https://form.jotform.com/200854658099972

Please check it out and let us know if this fits your requirements.