posted by ReRe .
Multiply using the rule for the product of the sum and difference of two terms. Assume any variable exponents represent whole numbers.
(x - y + 11)(x - y - 11)
Have you learned the rule that they are suggesting that you use? I strongly adise doing so. In this case, what you have is the sum and difference of the terms "x-y" and "11".
The general rule is
(a + b) (a - b) = a^2 - b^2
Please avoid name changes and the posting of long lists of questions with no work shown.