The coefficient of "-x" is: "-1" {"negative one"},
For "stand alone" variable, with coefficients of "1" or "-1", we often OMIT the "1" or "-1"; and just use the "+" (positive sign); or leave as written for positive; and just use the " - " (negative sign; with the "1", for negative); since any value multiplied by "1" is that same value; so the omitted "1" (or "-1"); in implied.
