Make 24 by using the following numbers only once: 1, 3, 4 and 6. You are allowed to add, subtract, multiply, divide and to use curly brackets. Do the same excercise with 3, 3, 7 and 7.

I'm in a zoo
But not in a jungle
I rarely come in pairs
But I'm in every puzzle


Some think I'm in a xylophone
But, I most certainly am not
You don't see me with a loan
But very strangely in a zealot


I'm in the magical prison of Azkaban
Well, can't you see?
I'm in the buzz of a fan
But, my oh my what could I be?

You've got two jars, one of them fits exactly 5 litres, the other one fits exactly 3 litres. How could you get exactly 4 litres with these two jars? It is allowed to spoil some water.