(a) to get a resistance of 4 ohm the resisistances 3 ohm & 6 ohm must be connected in parallel, and the resultant will be connected in series with the 2 ohm resistance.
1/ r = 1/3 + 1/6
= 3/6 = 1/2
r = 2 ohm
now, (2 + 2) ohm = 4 ohm is the reqd. resistance.
(b) three resisters of resistances 2 ohm ,3 ohm ,and 6 ohm should be connected in parallel to get a resistance of 1 ohm.
1/r = 1/2 + 1/3+ 1/6
= 6/6
r = 1 ohm
