Hi Victor, Google Forms does not support calculations or field permissions. You can customize your google form using the Neartail addon to calculate the amount and collect payments if needed. Please note that you must use the Neartail share link or the embed code to collect responses; otherwise, customization and calculations will not work. When use the Neartail link, the responses will be recorded in both Neartail and Google Forms. When you subscribe to the paid plan, you can choose between a monthly or annual option. The monthly subscription is automatically renewed each month, and you can cancel it at any time. If you cancel, the subscription will remain valid until the end of the current billing period. The annual subscription is a 12-month commitment and is non-refundable. If you only need it for a short term, it's best to choose the monthly plan, use it for 2 months, and then cancel before it renews for the 3rd month.