databases

I have a problem in implementing triggers for conditions as
schema of table given

ProjectMember (EmpID, FirstName, LastName, IsManager, BudgetAuthority)
Project (ProjectID, Title, Start, Deadline, First, Budget, Manager)
Task (TaskID, Name, Cost, Project, Assignee)
Schedule (Task, Successor)

implement triggers in POSTGRESQL for
Project.Budget = 1000 * sum (Project.Tasks.Cost) + 10%,
{ ProjectManager.BudgetAuthority >= sum (ProjectManager.Manages.Budget) }