I have no doors but I have keys, I have no rooms but I have space, you can enter but you can’t leave! What am I?

Replace the question mark with the number below given a simple math problem.

The Federal bank of London is abducted by the robbers. The head of the robbers asked the cashier to empty their money vault to them and when suddenly cashier got a call from her father. To avoid any suspicion, the robber asked the cashier to pick the call and reply her father in the shortest manner possible.

The cashier told her father "Is there an emergency father, Call me when you are free and I will help you in your furnishing" and then the cashier hung up the phone.

After 10 minutes, police arrived at the crime scene.

How did the police know about the robbery?

My thunder comes before the lightning; my lightning comes before clouds; my rain dries all the land it touches. What am I?

How can you take 2 from 5 and leave 4?

We know that the number 7 is the prime followed by a cube. Which next number is also a prime followed by a cube?

You are presented with three boxes. One of them has a red ball inside and the other two have a black ball inside each of them. You are asked to pick up the one with red ball and you pick one. Now, one of the other boxes is opened and it is found to have a black ball.

You are presented with a chance to change your box with the one that is left closed. Will you change your box? Why or why not?

Replace the question mark with the correct number in the below-given picture?

What is black when you buy it, red when you use it, and gray when you throw it away?

I have one of the three numbers: 1, 2, or 3 in my mind. I speak only truth. You can ask me just one question for which I will only reply in yes or no or don't know. What question will you ask from me so that you are able to know the number?