This property is called the distributive property. It is when you distribute the number outside the parenthesis into the numbers and letters inside the parenthesis.
Example:
7(x-3) = 7x-21
10(x+5+8) = 10x+50+80 = 10x +130
be sure to simplify like terms as in the example above
10 ( x²+5x³+2x²) = 10x²+50x³+20x² = 30x²+50x³
answer: 30x²+50x³
hope this helps