Q. Write down KCL equation for node A & node B.
Solution:
KCL equation
Sum of entering currents + sum of leaving currents =0
Now the equation of currents at node A & B by KCL
For node A
-I1+I2+ 3mA = 0 // I2 & 3mA are entering & I1 is leaving
For node B
-12mA + 4mA +I1=0 //12mA & I1 are leaving & 4mA is entering