The equation means that -28 is the number that you get when you subtract 12 from unknown number which has already being multiplied by 10. Therefore, we need to take this unknown number to be x so that our equation can be 12-10(x) = -28. We are multiplying x by 10 because we are told that 12 is subtracted from the unknown number 10 times. The answer then becomes 4 as 12-10x=-28 becomes -10x=-28-12 to get -10x=-40. Divide -10x on both sides so as to get x as 4.
Write it as an equation. The word "difference" indicates that you will subtract. The phrase "a number" means you will have an unknown. Let's call it n. 12 - 10n = -28. Add 10n and 28 to both sides to simplify your equation to 10n =40. Divide both sides by 10 to solve. n = 4.