These three inequalities must be held ("the triangle inequalities"): 1. 2x-1 <= (3x+2) + (12-x), which implies -1 <= 14, which is always TRUE. 2. 3x+2 <= (2x-1) + (12-x), which implies x <= 4.5. 3. 12-x <= (2x-1) + (3x+2), which implies x <= 1.5. Answer. All possible values of x are in this interval (0,1.5).