Write the following as triggers. In each case, disallow or undo the modification if it does not satisfy the stated constraint. The database schema is from the "PC" example of Exercise 2.4.1: Product (maker, model, type) PC (model, speed, ram, hd, price) Laptop (model, speed, ram, hd, screen, price) Printer (model, color, type, price) a) When updating the price of a PC, check that there is no lower priced PC with the same speed. b) When inserting a new printer, check that the model number exists in Product.