I think it is the third one. If it’s not the third one then it’s the first one.
(x cookies) / (23 students - (12/2) students) = 2 cookies per student
[x / (23 - 6)] cookies per student = 2 cookies per student
23 students * (2 cookies per students) - 12 cookies = x cookies
The "students" unit cancels
46 cookies - 12 cookies = x cookies
x cookies = 34 cookies
Just use pemdas
(Parenthesis, exponents, multiplication, division, addition, subtraction)