Mary solved the following problem:

[tex] 57 - 6^2 + (10 + 2) [/tex]
[tex] 57 - 6^2 + 12 [/tex]
[tex] 57 - 36 + 12 [/tex]
[tex] 57 - 48 [/tex]

Result: 9

Which of the statements is true?

A. It is wrong because [tex]6^2[/tex] is 12.
B. It is wrong because [tex]57 - 48[/tex] is 11.
C. It is correct.
D. It is wrong because the subtraction should have been done before the addition.

Let's analyze the expression step by step. The original expression is

[tex]$$
57 - 6^2 + (10+2).
$$[/tex]

1. First, we compute the exponent:

[tex]$$
6^2 = 36.
$$[/tex]

2. Next, we compute the addition inside the parentheses:

[tex]$$
10 + 2 = 12.
$$[/tex]

3. At this stage, the expression becomes

[tex]$$
57 - 36 + 12.
$$[/tex]

4. The proper order of operations (also known as PEMDAS/BODMAS) dictates that we perform the subtraction and addition from left to right. This means we first do

[tex]$$
57 - 36 = 21,
$$[/tex]

and then

[tex]$$
21 + 12 = 33.
$$[/tex]

Mary, however, proceeded by first combining [tex]$36 + 12$[/tex] to get [tex]$48$[/tex], and then computing

[tex]$$
57 - 48 = 9.
$$[/tex]

This is an error because it incorrectly groups the subtraction and addition. The subtraction should have been performed before adding [tex]$12$[/tex].

Thus, the mistake is that the subtraction should have been done before the addition.