Final answer:
The expression 3(7v + 7) uses the Distributive Property, multiplying each term in the parentheses by 3 to get 21v + 21.
Step-by-step explanation:
When you see the expression 3(7v + 7), the mathematical property being used here is the Distributive Property.
This property states that multiplying a sum by a number is the same as multiplying each addend in the sum by the number and then adding the products.
To apply the distributive property to this expression, you would multiply both terms inside the parentheses by 3, which would give you 3 × 7v + 3 × 7, resulting in 21v + 21.