controls over transaction question, can someone help answer that

A company pays its employees a basic wage and often extra amounts for overtime
worked. Payments are made and other information is collected on the basis of time-sheets
that are completed weekly by each employee.
Describe controls that the company could use to ensure that:
(a) All overtime has been properly worked
(b) A time sheet is obtained from each employee
(c) The total hours on each time sheet have been correctly added up.