Yes, I get 300 V and 50 ohm on the right then (if I remember correctly to do that) and this gives me 3A running. But, can you spot any mistake in my equation.
It works good if I use -6, that gives V = 150 V or if I use other methods but I remember making this same mistake a year ago. I think I am missing something fundamental. I don't want to repeat it when solving complex circuits.
In circuit analysis we can use different methods. Usually source conversion and mesh analysis is easy to do. I have solved by source conversion.
In mesh analysis, assign one current to each mesh and apply Kirchhoff law to find the current in each mash.