When 50 V is applied to four series resistors, 100 µA flows. If R1 = 12 kΩ , R2 = 47 kΩ, and R3 = 57 kΩ, what is the value of R4?

• 38.4 kΩ
• 3.84 kΩ
• 384 kΩ
• 3.84 MΩ