A circuit is constructed with six resistors and two batteries as shown: The battery voltages are V1 = 18 V and V2 = 12 V. The positive terminals are indicated with a plus sign. The values for the resistors are: R1 = 60 Ω, R2 = 97 Ω, R3 = 90 Ω, and R4 = 93 Ω. The positive directions for the currents I1, I2, and I3 are indicated by the directions of the arrows.
What is V4, the magnitude of the voltage across the resistor R4?