Explain formula and answer! Thank you in advance!

The schematic below shows two batteries with negligible internal resistances ri and r2 connected to a network of three resistors. E R2 Ra 12 E2 The resistances are R1 = 1.98 02, R2 = 5.58 0, and R3 = 7.79 ( with r1 = 12 = 0, while the two emfs are E1 = 11.8 V and E2 = 6.08 V. Given these three non-zero resistances and two emfs, what current (in A) has to flow through R1, the resistor at the center of this network