Mr. Lin writes the expressions -20 - 8 and 8 - (-20) on the board.
He asks his class which result is greater. How can his class decide without finding
the value of each difference?

Just see that the first expression has all negative, meaning the total will be a negative, but the second expression the subtraction sign and the negative sign are together, there's a rule when two negative sign's are together/next to each other, they turn into a addition sign, so it basically 8 + 20 for the second expression, so 8-(-20) has a higher result

Step-by-step explanation:

There's no work needed to be done :P

you can first factor out the n to get n(1+5). we know that 1+5 is 6, so we just have 6n.