solving circuits

Parallel circuit: 
total resistance: 1/Rt = 1/R1 + 1/R2 + 1/R3
intensity: It=V/Rt
V in every resistor: I1*R1; I2*R2 ; I3*R3
I in every resistor: I1=V/R1 ; I2=V/R2 ; I3=V/R3
Voltage drop: V=I*R ( V is the same in every resistor)

Series circuit:
total resistance: Rt= R1+R2+R3
intensity:  It=V/Rt

V in every resistor: V1=It*R1 ; V2=It*R2 ; V3=It*R3

I in every resistor:  in every resistor= It

Voltage drop: V=I*R

to calculate the total resistance you add them normally (Rt= R1+R2+R3)

Mixed circuit:

total resistance: Rt= Rbc+Rdi+Rkj and 1/Rdi = 1/Ref + 1/Rgh

intensity: It=V/Rt

V in every resistor: Vbc= It*Rbc; Vef= It*Rdi; Vgh=Rdi*It; Vkj=It*Rkj

I in every resistor: Ibc=Vbc/Rbc; Ief=Vef/Ref; Igh=Vgh/Rgh, Ikj=Vkj/Rkj

Voltage drop: V=I*R

To calculate the total resistance you need to calculate the Rt between D and I using the method of 1/Rdi = 1/Ref + 1/Rgh. then you add the other resistance ( 8 and 6) to the answer.
To calculate the intensity you use the Ohm's law, 12v/Rt