Six light bulbs are connected in series with a 9.0 volt battery. What is the voltage across each bulb?

Voltage adds in a series and the amount of voltage dropped due to each resistor in a circuit (the light bulbs are resistors) depends on the resistance of each.

Assuming equal resistance of each light bulb, the voltage dropped on each is equal and should add up to 9V (Kirchoff's Rules).

So 9V/6 = 1.5V per light bulb.