[oopic] Basic electrical calculations

Hi my electronic fellows:)

I have a very simple question about some basic electrical calculations.

I need to know how to calculate the amount of watt and the amperes
drawn if i set up a circuit with two light bulbs with the following
charateristics in series (I will like to get the calculations for the
bulbs individually and for the whole circuit).

Light bulb X: 12V 5 Watts
Light bulb Z: 12V 10 Watts

The power supply is set to 12 volts.

As i get it. Light bulb X will draw 0,42A and bulb Z will draw 0,83A
but I'm in doubt wether or not if i should add the two numbers(amps)
together getting a total of 1,25A and use this number in the following
calculations, like this.

P = V * I

12 * (0,42 + 0,83)

Resulting in a total amount of 15 watts. Is that correct?

Finnaly, how do I calculate the need of a resistor?

Thanks in advance...

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