Question 17668
Hello There:

I'm going to assume that the letter 'X' means multiplication instead of representing a variable.  In the future, you should consider using an asterisk to denote multiplication, since the letter x is used almost exclusively as a variable.

Having said this, I will retype your expression:

21 * 2 - 54 / 9

The order of operations tells us to do multiplication and division before doing addition and subtraction.

So, working from left to right, we first need to do 21 * 2 and 54 / 9.

21 * 2 = 42

54 / 9 = 6

Substituting these values into your expression leads to:

42 - 6

So, the final result is 36.

~ Mark