The figure shows a circuit with three batteries and four resistors. Determine the magnitude of the current through resistor R if the battery emfs and resistances are: 81 = = 21 V, & = 14 V, &; = 19 V, R1 = 7 0, R2 = 4 0, R; = 2 0, and R4 = 4 0. R1 + R2 13 W RA