Use the formula S=(n-2)180. Since it's a decagon with 10 sides, n=10 --> S=(10-2)180=8*180=1440 so the sum of the interior angles of the decagon is 1440 degrees. The sum of all the angles listed plus x must be 1440, so we have the equation 1440=x+1200 (I just simplified all those). Solving you get \(x=\boxed{240}\)
.
