Open that PDF to Chapter 3, Section 3.2 (Nodal Analysis) . Draw the first circuit. Write KCL. Solve for the node voltages.
Simply downloading the file is not enough. To truly master the material, follow this study strategy: Network Theory By Alexander Sadiku.pdf
Network theory, also known as circuit theory, is the study of the behavior of electrical networks. It provides a fundamental understanding of the principles and analysis techniques used to design and analyze electrical circuits. The book "Network Theory" by Alexander Sadiku is a comprehensive resource that covers the fundamental concepts of network theory. Open that PDF to Chapter 3, Section 3