23) 0.41 A; 0 V
24) 18-V battery: 17.4 V; 12-V battery: 13.3 V
25a) -25.7 V
25b) 80-V battery: 77.4 V; 45-V battery: 43.3 V
26) 0 V
27) through R1: 0.68 A, left; through R2: 0.40 A, left
28) through R1: 0.60 A, left; through R2: 0.33 A, left
29) through R1: 0.13 A, right; through R2: 0.31 A, left; through R3: 0.18 A, up
30) through R1: 0.13 A, right; through R2: 0.31 A, left; through R3: 0.18 A, up
31) through 2 Ω: 0.26 A; through 6 Ω: 0.028 A; through 8 Ω; 0.29 A; through 10 Ω: 0.26 A; through 12 Ω: 0.29 A