Celia is asked to solve the system of linear equations {−2x+2y=−63x−4y=0 using substitution. Following is an outline of her work.

Step A: Rewrite –2x+2y=−6 as y=x–3.

Step B: Substitute y=x–3 into 3x–4y=0 to get 3x–4(x–3)=0.

Step C: Solve for x and find x=12.

Step D: Substitute this value in the equation y=x–3 to find y=9.

Step E: The solution of the system is (12,9).

Determine if her work is correct. If it is incorrect, select the answer that corrects the first step with a mistake.

a. Her work is incorrect. In Step B, she should have substituted y=x–3 into –2x+2y=−6.
b. Her work is incorrect. In Step D, she should have solved y=x–3 to get y=–3.
c. Her work is incorrect. In Step E, she should have interpreted the solution to be (9,12).
d. Her work is correct.
e. Her work is incorrect. In Step C, she should have solved 3x–4(x–3)=0 to get x=−127.
f. Her work is incorrect. In Step A, she should have rewritten –2x+2y=−6 as y=6.