Rhonda is only half way right. Yes, it could take on any value, but it wouldn't be a negative. The absolute value is what the distance is from that number to 0 on the number line. Even though it is negative, it would still be a positive number. For example, l3l has a value of 3. In the same way, l-3l has the same value because they are both the same distance from the number line.
We know that 3r-6=3(r-2) because 3*r is the same as 3r and we know that 3*-2 is -6 hence making them equal. And to check it we know that 3r-6 is equal to 3r-6.