The best way to approach a question of this nature is by applying the rule of BODMAS. Just a quick reminder, that means Bracket of Division, Multiplication, Addition and Subtraction.
Observe that the numbers in the parenthesis have a minus and a plus sign, and the question of which to take before the other now arises. So we'll take the addition first before the subtraction.
Start with the smaller parenthesis inside the larger parenthesis. The solution to that is (5-4)^9 which is 1^9. One raised to the power of nine is one, that is;
1^9 = 1
So what you have in effect is;
18/ [8 - 6 + 1]
That effectively becomes
18/ [8 - 7]
18/1
That equals 18.
**Note that the values 8 - 6 were not put in parenthesis, and hence we had to apply the rule of BODMAS. If they had been separated by another smaller parenthesis, then the result would have been [8 - 6] + 1^9 which would be 2 + 1.**