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 + sign, the values for the resistors are: r1 = r5 = 58 Ï, r2 = r6 = 124 Ï r3 = 47 Ï, and r4 = 125 Ï. the positive directions for the currents i1, i2 and i3 are indicated by the directions of the arrows. 1) what is v4, the magnitude of the voltage across the resistor r4?