Answer
$20$
Work Step by Step
Absolute value is used to represent the distance of a number from $0$ on a number line. Since distances are always positive, the result of an absolute value will always be positive. Therefore, to take the absolute value of a negative number, we simply take the negative of that number to make it positive, and to take the absolute value of a positive number, we do nothing to the number. We simplify inside the absolute value symbols by subtracting and then remove the symbols in accordance with the rules for absolute values: $$|-9-11|=|-20|=20$$
