If the sum of a number and ninenine is doubleddoubled, the result is oneone less thannbsp the number. find the number

"the sum of a number and eight is doubled, the result is one less than the number"
                     (      x       +         8  )       *     2                    =            -1          +    x
Rewrite:
        (x+8)*2 = x-1
         2x + 16 = x-1       (distribute the 2)
         x +16 = -1             (subtract x from both sides)
         x = -17                 (subtract 16 from both sides)
 
Checking (very important):
   Is (-17+8)*2 = -17-1     ?
          -18        = -18       ?    yes.