Solution:

SH

Explanation :
If you look closely, you will see that the first letter of every set is moving 6 alphabets forward while the second one is moving six alphabets backwards.

Solution:

It is possible that the man was a deep sea diver. Such divers must wear a pressurized suit to withstand the pressure in the depths of the sea. If it tears down accidentally, the person will die. But for a short period of time, the breathing apparatus can keep him alive.

Solution:

You must be aware of the fact that the standard weighing system is Imperial system. This is how we weigh things or ourselves and thus the warning must be for 130 pounds according to the Imperial system.

But gold is weighed in the Troy system. In Troy system, 12 ounces makes one pound whereas in Imperial system, 16 ounces make one pound.

Thus 40 pounds (20+20) of gold bars will be 30 pounds in imperial system. The weight of thief is 100 pounds. Thus, the total is 130 pounds which can be accommodated on the rope and thus he was able to cross safely.

Solution:

Quadratic

Explanation:

quad(4 wheeler)
+ rat
+ i (eye)
+ C

Solution:

245

space them properly as 21 24 27 30 33 36 39 42 45 ?

Solution:

-20

Its a alternate series riddle
60 40 20 0 (?)
40 43 46 49 (+3)

Solution:

Mercury

Solution:

Be inspired (B in Spired).

Solution:

A Telephone

Solution:

11