Step-by-step explanation:
Find the EQUIVALENT resistance of the parallel R2, R3 and R4 :
1/ ( 1/50 + 1/30 + 1/60) = 14.29 Ω
Now find the current through the series circuit of 75 and 14.29 ohms :
V/R = I 12 V / ( 75 + 14.29) Ω = .1344 A
Now the voltage drop across R1 is : I * R = .1344 ( 75) = 10.08 v
the remaining 1.92 v is applied (and dropped ) across each of the other R2, 3 and 4 resistors
current R2 is V / R2 = 1.92/50 = .0384 A
R 3 current is V / R3 = 1.92/30 = .064 A
R 4 current is V / R4 = .032 A