完成7.6.2 节中对雇员工资计算程序的扩充，即将一般雇员再细分为计时雇员(DailyWorker)和计件雇员(PieceWorker)两类，计时雇员按天计算工资额，而计件工资按其生产的产品件数计算工资额。请设计这两个类，并与程序7.11 至程序7.13 结合在一起，然后类似程序7.14 编写一个演示程序，演示这些类的用法。-Section 7.6.2 to complete the calculation of employees'　wages to expand the program, employees will generally subdivided into time employees (DailyWorker) and piece-rate employees (PieceWorker) categories, time wage employees by day, and their production of piece-rate wages Product Number calculating wages. Please design of these two classes, and programs and procedures 7.11 to 7.13 together, and then write a similar program 7.14 demo program that demonstrates the usage of these classes.