John is correct. The substitution property is being used. The x is being substituted for the value 9 (aka x is replaced with 9). Keep in mind that x is simply a placeholder for a number, in this case 9.
Think of "substitution" as in a sports game where one player replaces another. Or you can think of a substitute teacher where someone else temporarily replaces your teacher for the day. Those are two ways to help remember the term.
The distributive property is not being used here since it is a*(b+c) = a*b+a*c. For example, 2*(3+5) = 2*3+2*5
Every kilogram is 1,000 grams, but you want 10 kilograms. You can multiply 1,000 10 times (you can also add 1,000 10 times,) giving you the answer > 10,000.
