Question

You replace a 200 W lamp with a more efficient 55 W LED lamp. If you leave your lights on 24 hours a day, how much energy are you saving each day by replacing this bulb?

Answer 1

Watts (W) is actually a unit disguised as joule per second.
To find energy (in joules) we take the amount in watts multiplied by the time it is switched on (in seconds since we are using watts!).
Finding the energy (in joules) for both builds and taking the difference should give you the answer.