Question 528973
This is a small questions within the directed numbers:

8-8n-10n: we will ignore the 8 for now since it is already seperated
-8n-10n: these are all negative numbers(or unknowns), I need you to remember these:

+,+=+
+,-=-
-,+=-
-,-=+

or you could just remember same symbols are positive, different symbols are negative.

And calculations on addition and subtraction:

if the numbers' following symbols are the same, they adds and will copy down the symbol:
E.g. -1-1=-2

if the numbers' following symbols are different, they subtracts and will copy down the symbol of the larger number (if they are same the answer will always be 0)

E.g 1)-8+10=+2
    2)-7+7=0

According to these:

 -8n-10n
=-18n

And:

 8-8n-10n
=8-18n