Twice the difference of a number and 4 is 9

Answer 1

Let "n" be the number then "the difference of the number and 4" would be either n - 4 or it could be 4 - n

Let's take the first case (n - 4). Twice that difference would be 2(n - 4) and setting it equal to 9 gives us 2(n - 4) = 9 or 2n - 8 = 9, or 2n = 17 or n = 8.5

Taking the second case (4 - n), 2(4 - n) = 9 becomes 8 - 2n = 9 or -2n = 1 or n = -0.5

Either of those answers would work depending how you interpret "the difference of the number and 4".

Answer 2

2(n - 4) = 9

Is that all you need?