Current and voltage source equivalent circuit?

Here, it talks about bridging the resistor, but I don't see any bridging because the current source IC was replaced by an open circuit. So, the current must return via R6, and no bridging took place. Why is bridging mentioned here? Additionally, I don't understand how the resistors can be short-circuited by the beta node?…

Calculate the desired voltage by summarizing the sources?

Hello, I need help with a simple circuit: In order to get to Ua you would actually first have to combine the sources. Normally it would be a good idea to convert the 6 V voltage into a current source, but the 5 Ohm resistor is in parallel…. It is explicitly stated that the problem…