What property is being used for 8x-2+x-14 and 9(4m+1) and lastly 3(-2x+7) i already know the answers for those, i just need with the question that says "what property is being used for those problems"

How many liters of peroxide should be added to 12 liters of an 8% peroxide solution so that the resulting solution contains 16% peroxide?   original added new amount of peroxide 0.96 liters x 0.96 + x amount of solution 12 liters x 12 + x 0.18 liter 1.14 liters 1.92 liters 2.10 liters