As a result of several weeks of employees working many overtime hours, it becomes obvious to you and your project managers that you're not going to be able to catch up to where you should be in the schedule and that you're going to have to ask your customer for an extension to the delivery schedule. One of your project managers says she'll call up the customer ask for more time and that it shouldn't be a problem. How do you explain to your project managers what the correct things that must be present get a legally binding contractual modification extending your delivery time?