Answer:
Line E
Step-by-step explanation:
Given
The instructions in the question
Required
The first line of mistake
The question has missing details, as the original expression is not given;
Reading through the question, one can observe that, Mary made a mistake at Line E.
The expression on D is:
[tex]23 - 6 + 9[/tex]
The expression on E is:
[tex]23 - 15[/tex]
The actual result of D is:
[tex]23 - 6 + 9 = 23 + 3[/tex]
not
[tex]23 - 15[/tex]
Because:
[tex]-6 + 9 = 3[/tex]
[tex]-6 + 9 \ne 15[/tex]
With the available information, we can conclude that Mary's first mistake is at line E