Answer: 20 liters
Step-by-step explanation: Let x represent the amount of 10% solution used. Let y represent the amount of 25% solution used. Since 30 liters of 15% solution are being made, our first equation is x + y = 30.Now we deal with the actual peroxide in each solution. x liters of 10% peroxide contain 0.1x liters of peroxide. y liters of 25% peroxide contain 0.25y liters of peroxide.30 liters of 15% peroxide contain 0.15 * 30 = 4.5 liters of peroxide. From this information, we can write our second equation.0.1x + 0.25y = 4.5We have a system of equations: x + y = 300.1x + 0.25y = 4.5Multiply the first equation by -0.25 and add to the second equation.-0.25x - 0.25y = -7.5 0.1x + 0.25y = 4.5-------0.15x = -3x = 20