Top left: 2 series;Voltage regulator. R2/R1+R2.
Top right: voltage regulator + parallel.
(1/(1/R2+1/R3))/(R1+ (1/(1/R2+1/R3)))
Mid left: parallel resistors. (1/(1/R1+1/R2))
Bottom right: 2 voltage regulators+parallel.
R3+R4=RR, (1/(1/R2+1/RR))/R1+(1/(1/R2+1/RR)))
the bottom 2 are just me messing around with adding them together.
