(a)to find voltage of battery we use the wire containg 4 ohm resistor and 3 ohm resistor
the voltage of 4ohm = Ri=4x1.5=6V
the voltage of 3 ohm = Ri=3x1.5=4.5v
since voltage is additive in series then Voltage of batteries = 4.5+6=10.5V
(b) the currrent flowing in 20 ohm resistor is the same as 8 ohm resistor so
Voltage of 8 ohm + voltage of 20 ohm= 10.5
8i+20i=10.5
28i=10.5
i=0.375 A