tolong bantuannya ya no 7a please

yg paralel dulu cari
yaitu :
1/Rp = 1/R1 + 1/R2 + 1/R3
1/Rp = 1/15 + 1/15 + 1/15
1/Rp = 3/15
Rp = 15/3
Rp = 5
trus seri,,,,,
5 + 5 + 5 15 ohm