You can put this solution on YOUR website!
In this case you would use less than 25.
If you used not equal to 25, you would have a two-tailed test, and it would include the situation where the average life of the light bulb was less than 25 hours, but would also wrongly include the situation where the average life of the light bulb was MORE than 25 hours.
So you want to use the one-tailed case, where the alternative hypothesis is checking for the average life of the light bulbs less than 25 hours.
This is a case where you have to use real world logic when setting up your hypothesis test, because the consumer protection agency would never accuse a manufacturer of fraud if their light bulbs lasted LONGER than the manufacturer says they should.
For example, if an auto parts maufacturer says their Economy car battery lasts 3 years, no one would complain if the Economy car battery they purchased from that specific manufacturer lasted 5 years! :)
I hope this helps.