Pke cara??.............

I = V/R
I = 3 / (12+8+10)
I = 3 / 30
I = 0,1 A

Daya (P) = V . I
P = 3 . 0,1 
P = 0,3 Watt

R1 = 12Ohm
R2 = 8Ohm
R3 = 10Ohm
V = 3V
P = ........?

P1 = V²/R1
= 3²/12 = 9/12 = 3/4 = 0.75 Watt
P2 = V²/R2
= 3²/8 = 9/8 = 1.125 Watt
P3 = V²/R3
= 3²/10 = 9/10 = 0.9 Watt