X - 5-X\2 - 12X\4 = 21 4X|4 - 2*(5-X)\4 - 12X\4 = 21 4X -(10-2X) - 12X = 21*4 4X - 10 +2X - 12X = 84 -6X = 94 X = - 15,666 = - 15,7