The distributive property....u r basically multiplying the number outside of the parenthesis by everything inside the parenthesis...this gets rid of the parenthesis.
3(-4x + 8)...distribute the 3 thru the parenthesis (3 * -4x) + (3 * 8) ...take that 3 and multiply it by every number in the parenthesis..to get rid of the parenthesis -12x + 24 <===