Question

Can somebody please tell me how do you know who solving through node analysis which current to subtract to which one when all of them are given in terms of variable??

Answer 1

Actually the example is Loop/Mesh analysis, for this analysis you need to find an appropriate tree, maximum number of branches with no loops. Each branch removed would be a chord, variable current would go through it. It make sense to make the 6A and 8A current sources chords because their known current. This leaves the 6 ohm resister left for the third chord, 6A and 8A chord's isolated. By convention loop currents are taken to be positive in the counter clockwise direction. Write one equation about 2, 6, 8 ohm resistor, considering all sign rules, when going + to - across a component consider the voltage positive, - to + voltage negative, This will correspond to KVL the sum of the voltage around a closed path is always zero.

Answer 2

My best guess when dealing with such problems is to think of KCL as; the total number or sum of current entering the first node is equal to the total number living so, you can form your equation from there