please answer the question below

In the gure above, R3 is to be adjusted in value by moving the sliding contact across it until points a and b are brought to the same potential. (One tests for this condition by momentarily connecting a sensitive ammeter between a and b; if these points are at the same potential, the ammeter will not deect.) Express R1,. in terms of R5, RI and R2 in the case when this adjustment is made. In thegure the current in resistance 6 is is = 1.41 A and the resistances are R1 = R2 = R3 = 2.44 0, R4 = 16.5 0, R5 = 8.42 D, and R6 = 4.21 Q. What is the emf 0f the ideal battery? Number n : Units V