d) List two functional and two non-functional requirements for the systems described below. Your requirements must be describing a key aspect of the listed systems and non-functional requirements must reflect tangible and measurable expectations. Non-functional requirements such as The system must be fast will not be given any marks. i) A cross-platform instant messaging application (such as WhatsApp) ii) Website of an electronic commerce company (such as Amazon) iii) A graphic design software (such as Adobe Photoshop) iv) A flight controller system for airplanes (software on board of airplanes) [8 Marks] e) Discuss the main differences between waterfall and spiral models. [8 Marks]