a b c d

d

$\text{Let Resistance of each bulb is R} P = \frac{V_0^2}{R}$  $\text{ Since Three bulbs are similar Voltage across each bulb is }\frac{V_0}{3}$ $ P_1 = \frac{V_0^2}{9R}$ $ P = 3P_1 = \frac{V_0^2}{3R} = \frac{P}{3} = \frac{60}{3} = 20W$