Railroad Crossing, look out for the cars. Can you spell that, without any R's ?

A red house is made out of red bricks. A yellow house is made out of yellow bricks. And, a blue house is made out of blue bricks. So, what is a greenhouse made of?

How will you measure 15 minutes using two hourglasses of 7 minutes and 11 minutes respectively?

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

Can you find out the number that should replace the question mark with a valid reason?

A mother is 21 years older than her child. In exactly 6 years from now, the mother will be exactly 5 times as old as the child.
Where's the father?

What is the largest amount of money that you can possess in change and still if someone asks you for a dollar, you won't be able to give?

There are 2 people near the river and both of them want to get on the other side. The boat can only take one of them. But they got across.
How?

I have four wings but can't fly.
I express no emotions.
I am found on the exact spot every time you look.
I keep toiling away with a little sound.

Do you know what am I?

Solve the mathematical equation in the picture below.