Answer:
-9
Explanation:
To answer this question, you have to know how to translate what is asked in words into equation form.
The word difference means subtractions. For example, the difference of 8 and 3 is 5. In equation form, this means " 8 - 3 = 5 "
To say "twice a number" means to have a number twice, which is multiplication. Since we don't know what the number is, we will call it x.
So to put the proposed question in equation form, we would say "2x - 3 = -21"
Now that we've got the equation, we can now solve for x. To do this, we group the like terms first. In this case it's -3 and -21. The easiest method would be to move the -3 to the other side of the equals sign, but in order to do this we have to change the sign of the -3. So your equation now looks like this
2x = -21 + 3
At this point, we add -21 and positive 3, which equals -18, so now we have
2x = -18
Now, in order to get x by itself, we need to look at the main operation on the left side of the equation. The main operation is multiplication because "2x" really means "2 multiplied by x". So in order to get x by itself, we need to move 2 over to the other side of the equation. Since division is the opposite of multiplication, we divide both sides by 2. If we divide the left side by 2, we are left with x by itself because 2 divided by 2 =1, meaning we have 1x, or simply put, just "x".
However on the other side of the equation, we divide that as well by 2. So -18 divided by 2 is -9
The answer is x = -9