The voltage across all resistances is the same:
V=I1R1=I2R2=I3R3.
By Kirchhoff's current law:
I1+I2+I3=90 A. R1V+R2V+R3V=90 A.
The resistance of each resistor is
R1=πr12ρL1, R2=πr22ρL2=π(2r1)2ρ(23L1)=83R1, R3=πr32ρL3=π(3r1)2ρ(2L1)=92R1.
Since I1R1=I2R2=I3R3,
I1=83I2=92I3, I1+38I1+29I1=90, I1=11 A,I2=29 A,I3=50 A.
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