write a function to calculate and return the amount of a salesman is making his/her commission rate stored in the employee table. HINT: You must pass the employee name and sales amount, and the function returns the commission amount calculated based on the commission rate stored table. The table was created using:

CREATE TABLE employee(

empname VARCHAR2(20) PRIMARY KEY

,startdate DATE NO NULL

,commissionrate NUMBER (3,1)

,title VARCHAR2(26)

,manager VARCHAR2(20) REFERENCES employee (empname)