What does the below rebus riddle means?

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

What can you see in the middle of March and April that you can never see in any other month?

I have cities, but no houses. I have mountains, but no trees. I have water, but no fish. What am I?

If you say my name, I will no longer exist. What am I?

What can run but never walks, has a mouth but never talks, has a head but never weeps, has a bed but never sleeps?

Cristina was born in 1888. She just had her 30th birthday today how did that happen?

In an office's desk, you find a unique method that shows the current day of the month. Two numbered cubes are used to depict the current date.

Can you find out the numbers on both the cubes so that each date can be mentioned using them?

Please note that you have to use both the cubes to display any date. Thus the 1st day must be represented by 01 and so on.

A mules travels the same distance daily.
I noticed that two of his legs travels 10km and the remaining two travels 12km.
Obviously two mules legs cannot be a 2km ahead of the other 2.

The mules is perfectly normal. So how come this be true ?

There are 2 sand hourglasses.

The small one can measure 5 hours and the large one can measure 7 hours.

How can we measure 16 hours with 2 sand hourglasses running together ?