A number decreased by the total of the number and fourteen

The answer to this would be x - (x+14)

Here's an explanation:

Let x represent the unknown number. The problem says that x has been decreased by the sum of x and 14. So, to put this in a form of an equation, it would be x - (x+14), since you have to do the addition first before you can subtract the two number since you don't know what x is. This equation is equal to - 14 no matter what x is.