Need on a question for my correction, if u know it !

Which simplifys to a+ b? a-(1-b)+1 -(1-a)-b+1 (a--1) -1)+1

How many different three-digit numbers can be formed using the digits 1 comma 2 comma 9 comma 6 comma 4 comma 3 comma and 8 without repetition? for example, 664 is not allowed.

Asequence has a common ratio of and f(5) = 81. which explicit formula represents the sequence? f(x) = 24 f(x) = 16 f(x) = 24 f(x) = 16