6. An electrical circuit is shown below. The battery supplies 15 V. The resistances have the following values: R1=300,R2=400,R3=200. (a) Calculate the replacement resistance of the three resistors. (b) Calculate the total current through the circuit, and the current through the respective resistor (c) If the lower right corner is grounded, then calculate the potentials at points A and B. (d) If the current is interrupted at point C, what will be the potentials at A and B