if the average ( arithmetic mean ) of x + 1 , x + 5 , and x + 9 is 0 , then x =
"( x + 1 + x + 5 + x + 9 ) / 3 = 0 = > 3 x + 15 = 0 = > x = - 5 answer a"
subtract(multiply(5, const_2), multiply(1, const_2))