negative x subscript 15 minus x subscript 25 plus x subscript 35 plus x subscript 45 equals negative 280 negative x subscript 15 minus x subscript 25 minus x subscript 35 minus x subscript 45 equals 280 x subscript 15 plus x subscript 25 plus x subscript 35 plus x subscript 45 equals negative 280 all of the above. none of the above