Eight of us go fourth, not back, to protect our king from an attack. What are we?

Solve this riddle by finding the odd one out from the rest.

Take 9 from 6, 10 from 9, 50 from 40, and leave 6.

How Come ??

Detective John was investigating a murder in China.
It was a difficult case, and John was completely stumped until he noticed a message sent to him by the killer cunningly hidden in a newspaper advertisement selling Car Licence Plates.
Detective John thought about it for a while, and when he had solved the puzzle, immediately arrested the guilty man.

Q1) How did John know the advert was a clue for him?

Q2) Solve the code and tell me who John arrested.

This is the newspaper advert (Car licence plates for sale) that Detective John saw.

Plates For Sale;

[W 05 NWO]
[H 13 HSR]
[O 05 EBM]
[D 08 UNE]
[U 10 HTY]
[N 04 BRE]
[N 16 TTE]
[I 26 LHC]
[T 10 AEE]
[I 26 CNA]
[X 22 VDA]

Can you identify the direction in which this bus is moving; left or right?

Hint: The bus is moving on the roads of London.

Many have heard it, but nobody has ever seen it, and it will not speak back until spoken to. What is it?

How many cubic feet of dirt are in a hole of one foot deep, three feet long, and two feet wide?

A shepherd had 18 sheep, out of which, all but ten died.

Can you tell us how many sheep was he left with?

Two boys wish to cross a river. The only way to get to the other side is by boat, but that boat can only take one boy at a time. The boat cannot return on its own, there are no ropes or similar tricks, yet both boys manage to cross using the boat.

How?

I am weightless, but you can see me. Put me in a bucket, and I'll make it lighter. What am I?