Meaning of the Hadith "extinguish your lamps" before going to sleep

Q: What's the ruling about extinguishing your lamps, how we understand it? 

It was narrated from Jabir ibn `Abd-Allah (may Allah be pleased with him) that the Prophet (peace and blessings of Allah be upon him) said: 

“When the wings of the night spread – or when evening comes – keep your children in, for the devils come out at that time. Then when part of the night has passed, let them go. And close the doors and mention the name of Allah, for the devil does not open a closed door. And tie up your waterskins and mention the name of Allah, and cover your vessels and mention the name of Allah, even if you only put something over them, and extinguish your lamps.” (Narrated by Al-Bukhari, 3280 and Muslim, 2012)

Giving a loan on interest

Q: Two parties want to enter an agreement: Person A wants to loan money to Person B. 

The amount is marked up by 10% and the repayment is over a fixed period e.g. 4 years. 

If there is a clause in the agreement to say that if you pay by 3 years, you will get R2000 back. 

Is the rebate of the R2000 clause permissible? Is the allocation of marked up shares permissible?

Zakaat on a lost gold ring

Q: My wife took out her gold ring to make wudhu at home and then forgot where she left it. This happened last week. 

We searched high and low for it, in the cupboards, drawers, and in every part of the house (in the kitchen, under the sofa, or any other place possible). 

After searching extensively, we have now lost hope of finding it, and we now suspect the helper may have snatched it. Will my wife need to pay zakaat on the ring?