Replace the question mark with the correct number, given the pair of numbers exhibits a similar relationship?

? : 3839 :: 11 : 1209

In a town, there are over 100 flats.
Flat-1 is named first flat.
Flat-2 is named second flat.
Flat-3 is named third flat.

A visitors 'Victor' decides to walk through all the flats, he finds all the flats except flat-62.
Victor later founds that the local of the town have given it another name.

What is the name of the Flat?

Can you solve this amazing hard number series problem?
7, 8, 10, 12, 16, 18 ?

What do you see in the image below

A chicken farmer has figured out that a hen and a half can lay an egg and a half in a day and a half. How many hens does the farmer need to produce one dozen eggs in six days?

Can you find out the smallest number that can be conveyed as the sum of three squares in three unique ways?

A word I know,
Six letters contain,
Subtract just one,
And twelve is what remains.

Decode below three cipher riddles:

26 L of the A
7 D of the W
1000 Y in a M

Doctor Alex and a bus driver John are both in love with the same woman named Olivia. The bus driver need to go for a long trip of 10 days, Before he left he gave Olivia 10 apples.

I know a country, If you remove the last alphabet of its name, it will become a part of your body. Do you name it?