Nomor 3 sama 5 minta tolong aja

R bc dan R cd, seri
R bcd = R bc + R cd = 5 + 15 = 20 Ω
R bd dan Rbcd, paralel
R' bd = (R bd * R bcd) / (R bd +R bcd) = (20*20)/(20+20) = 10 Ω
R' bd dan R de, seri
R bde = R' bd + R de = 10 + 6 = 16 Ω
R bde dan R be, paralel
R' be = (16*16) / (16+16) = 8 Ω
R ab, R' be dan R ef, seri
R af = 7 + 8 + 4 = 19 Ω
Kuat arus total = E /(R+r) = 20/(19 + 1) = 1 Ampere

Nomor 2
Rs = R/(n-1)
dimana n = I' / I = 0,6 / 0,1 = 6 kali
Rs = 500 / (6-1) = 100 Ω