Answer:
The number is -6
Step-by-step explanation:
We need to essentially "translate" this sentence into an equation. Let's break it down word by word.
"The difference of" means this is subtraction.
"Twice a number" means 2 multiplied by some unknown number. In math, unknown numbers are variables, so we can just call our variable "x". So twice a number means twice x, which is written as "2x"
"and 9". This means it would look like "2x-9"
"is -21" means "=-21" anytime you see the word "is" in these types of problems, it usually means that is the solution to the equation.
Now we have our equation, let's put it all together:
2x-9=-21
Now, solve for x accordingly, remembering PEMDAS:
2x-9=-21 First, isolate the variable. Get rid of the -9 by adding 9 to both sides
2x = -12 Continue to isolate the variable. Get rid of the 2 by dividing by 2
x = -6
