(a)where an employee's wages are the same for each pay period, a week's wages shall be the amount paid or payable to the employee in respect of a full working week under his or her contract of service as it applied immediately before the date of dismissal;

(b)where an employee's wages under his or her contract of service vary from one pay period to another according to the amount of work done by the employee during that period, a week's wages shall be the average wage received or payable in respect of a full working week by the employee, and the average wage shall be calculated by reference to the thirteen weeks of employment immediately preceding the date of dismissal;

(c)where an employee's wages under his or her contract of service vary from one pay period to another according to the total number of hours which he or she works during a particular pay period, a week's wages shall be the wages received or payable by the employee for a working week of an average length which shall be calculated by reference to the average number of hours worked in each week by the employee during the thirteen weeks of employment immediately preceding the date of dismissal.