Quickly Solve this riddle

7 - 4 + 3 * 0 + 1 = ?

No matter how little or how much you use me, you change me every month. What am I?

You have two strings whose only known property is that when you light one end of either string it takes exactly one hour to burn. The rate at which the strings will burn is completely random and each string is different.

How do you measure 45 minutes?

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?

Decode the below four famous ciphers:

8P of the SS
1M of the E
1S of the SS
60M in 1H

John is on an island and there are three crates of fruit that have washed up in front of him. One crate contains only apples. One crate contains only oranges. The other crate contains both apples and oranges.

Each crate is labelled. One reads 'apples', one reads 'oranges', and one reads 'apples and oranges'. He know that NONE of the crates have been labeled correctly - they are all wrong.

If he can only take out and look at just one of the pieces of fruit from just one of the crates, how can he label all of the crates correctly?

How can you make the following equation true by drawing only one straight line: 5+5+5=550 ?

What four weights can be used to balance from 1 to 30 pounds?

How can you take 2 from 5 and leave 4?

Christina has four daughters, and each of her daughters has a brother. How many children does Christina have?