Which property was applied to create this equivalent expression?

7 x + (5 + 6 x) right-arrow (7 x + 5) + 6 x
A. the commutative property only
B. the associative property only
C. the distributive property only
D. both the commutative property and the associative property

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