Let's say I have a list for saving the projects costs (Tasks), and each project in splitted into multiple parts (Subtasks), in these subtasks I have a custom field called "Cost" (From number type), and all subtasks having this field filled with the cost, I want the same field that is in the Main task to calculate the total value for his subtasks, and the same thing is for other custom fields, such as (Formula, Salary, Date, Number of people, Rating, Progress, )