Hi!
Let's look at "the difference of 19 and a number k".
"a difference" means subtraction, and that means that we subtract k from 19, so we have "19 - k"
Now, "11 less" also means subtraction, and it's 11 less than 19 - k, and therefore that is (19 - k) - 11, or simply 19 - k - 11.
Now, to simplify that, we can subtract 11 from 19, and your FINAL answer is than 8 - k.
Hope this helps! :D
