0.12x + 0.27*15 = 0.24*(x+15) ====> 0.12x + 0.27*15 = 0.24x + 0.24*15 ====> 0.12x - 0.24x = 0.24*15 - 0.27*15 ====> -0.12x = -0.03*15 ====> x = = 3.75. Answer. 3.75 liters of the 12% solution must be mixed with 15 liters of the 27% solution to get 0.24% solution.