Finding resistance of unknown resistors in 2 pairs of parallel circuits
Its easy you 2 parallel circuit attached in series.

First divided them into tow blocks 
First block is =
 ( R1*4ohms)/(R1+4ohms)
second block is =
(R1*R1)/(R1+R1)

after getting the result of the first block and the second block add them together it becomes something like this 
Rt=((R1*4)/(R1+4)) + ((R1*R1)/((R1+R1))
R1 have the same value.
Let's assume that you have the voltage and current. 

V=RT*I
............
RT=V/I
...........
RT-4 = new RT 
... ............
R1=new RT/3. = value of each r1