on my paper it says complete the equation, and tell wich property u used (3times10) times8=3times (10times8) but I don't know what the property is it

Property is a way to represent the same calculation in a different form. There are many kinds of properties:

- Commutative (Order) Property of Addition: a + b = b + a

- Commutative (Order) Property of Multiplication: a * b = b * a

- Inverse Property of Addition: a + (-a) = 0

- Inverse Property of Multiplication: a * 1/a = 1

- Identity Property of Addition: a + 0 = a

- Identity Property of Multiplication: a * 1 = a

- Zero Property of Multiplication: a * 0 = 0

- Associative (Grouping) Property of Addition: (a + b) + c = a + (b + c)

- Associative (Grouping) Property of Multiplication: (a * b) * c = a * (b * c)

The property from your example is the last one - Associative (Grouping) Property of Multiplication: (a * b) * c = a * (b * c). Let's check it:

(3 * 10) * 8 = 3 * (10 * 8)

30 * 8 = 3 * 80

80 = 80

Correct.