#### Answer

16

#### Work Step by Step

We need to use PEMDAS (Parenthesis, Exponents, Multiplication, Division, Addition, Subtraction) to find the correct answer.
1. The student followed the first rule of PEMDAS correctly and solved the parenthesis first. $23-8\times2+9$
2. The student performed the next step wrong by subtracting when he should have multiplied. $23-16+9$
3. The student should now add the positive numbers. $32-16$
4. Now, the student should subtract the numbers. $32-16=16$
The correct answer is $16$. The student made the mistake of not following PEMDAS and subtracting before he multiplied. By multiplying before subtracting, we were able to reach the correct answer of $16$.