How to calculate the voltage in this open circuit?
Hints


What does the 13 ohm resistor bring to the party?
What does the 9 ohm resistor bring to the party?
What effect does the 18 ohm resistor have on the 15V source?
What does the 4 ohm and 11 ohm bring to the party?
The voltage across the 10 ohm resistor is ONLY due to which current source?
Ditto the 5 ohm resistor
Simplify based on these hints.


The answer is 35V from a brief mental add-up of things - it is THAT simple (assuming I've read your scrawl correctly).