Answer:
correct answer is A
Explanation:
The diagram shows a series circuit with three resistors and two power sources.
In a series circuit the current through the entire circuit is constant and the resistance is the sum of the resistances in the circuit.
When the power sources are placed in opposite position the voltage between them is subtracted.
V_b - 30 = I (10 + 4 + 6)
V_b = I (20) - 30
V_b = 30 - 2 20
V_b = 10 V
the correct answer is A
