The problem is to determine the total resistance for the network. I came up with roughly 25 ohms, and I will detail each step. I am asking someone to verify this please. I am not sure if I needed to use any delta-wye transforms. The numbers are not "nice," unlike the other problems, so it is possible there is an error in my method, or not.
series resistors on far right (working towards nodes a & b)
(30 +60 +18) ohm = 108 ohm
108 ohm || 16 ohm = (1/108 +1/16)^-1 = 432/31 ohm
432/31 ohm in series with 28 ohm = (432/31 +28) ohm = 1300/31 ohm
1300/31 ohm || 40 ohm = (31/1300 +1/40)^-1 = 2600/127 ohm
2600/127 ohm series with 20 ohm = (2600/127 +20) ohm = 5140/127 ohm
5140/127 ohm || 24 ohm = (127/5140 +1/24)^-1 = 30,840/2047 ohm
30,840/2047 series with 25 ohm, 10 ohm = 30,840/2047 +25 ohm +10 ohm = 102,485/2047 ohm
102,485/2047 ohm || 50 ohm = (2047/102,485 +1/50)^-1 = 241,409/9650 ohm ~= 25 ohm
I thought it would be too cluttered to include a re-drawn circuit at each step. I worked from right to left in the picture only making series and parallel simplifications. I was not sure if a delta to wye transformation was needed, since I missed class due to health reasons that day. Any help is welcome. Thanks for reading. See you soon.