What 4-letter word can be written forward, backward or upside down, and can still be read from left to right?

Find the next number in the series below

21 32 54 87 131 ?

Replace the (?) with the correct mathematical signs to make the expression equal to 59.

18 ? 12 ? 4 ? 5 = 59

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

What's the only room from which no one can enter or leave

He does not have any heart but still, He manages to live.
If you kill him, you will eventually die but yet you kill him.
He cannot run, who is He?

If 21x = 79x, what is the value of x?

I am thinking of a five-digit number such that:
The first and last digits are the same, their submission is an even number and multiplication is an odd number and is equal to the fourth number. Subtract five from it and we obtain the second number. Then divide into exact halves and we get the 3rd number.

What number I am thinking of?

If,

20 % 5 = 24

21 % 7 = 33

42 % 6 = 67

Then;

66 % 6 = ?

I can be cracked, made, told, and played. What am I?