you combine like terms in this problem so in this case you do 18. and -5n and combine them. ALWAYS take the sign in FRONT OF the number whether it's plus or minus sign. If there is no sign it's a plus sign. So you to 18n-5n which is 13n the n stays the same. Now you have only +13 left so you just leave it since there is no other numbers without variables. your answer is 13n+13.