Q: Write down KCL equations for all of nodes.
Solution: KCL equation
Sum of entering currents + sum of leaving currents =0
For node A 10mA & 60mA are entering the node & the source current is leaving
For node A
It -60mA - 10mA= 0
And for node B
60mA - 40mA - 20mA = 0 // hear 60 mA is entering and 40mA, 20mA are leaving