Answer
$P = 11.111W$
Work Step by Step
First calculate the resistance of the bulb.
$P = V^2 /R$
$100 = 110^2/R$
$R = 121$Ohms.
Since the bulbs are connected in series, and there are three bulbs, the voltage across each bulb will be a third of the source voltage, so
$P = (110/3)^2 /121$
$P = 11.111W$