Answer
$23-8*2+9$ is not equal to $15*2+9$
$23-8*2+9=16$
Work Step by Step
Order of operations means that 8 must be multiplied by 2 first. The student solved the expression left to right, ignoring order rules, leading to the mistake.
$23-8*2+9=23-16+9$
$23-16+9=7+9$
$7+9=16$