Write the code for the following triggers following the style shown in the text.
a. When adding a customer, add the customer’s balance times the sales rep’s commission rate to the commission for the corresponding sales rep.
b. When updating a customer, add the difference between the new balance and the old balance multiplied by the sales rep’s commission rate to the commission for the corresponding sales rep.
c. When deleting a customer, subtract the balance multiplied by the sales rep’s commission rate from the commission for the corresponding sales rep.