Answer:
She wrongly added the equations
Step-by-step explanation:
Given
[tex]-3x + y = 8[/tex]
[tex]-3x + y = -4[/tex]
Required
Her mistake
The mistake is when she added the equations.
When both equations are added, the result is:
[tex]-3x -3x + y+y=8-4[/tex]
[tex]-6x +2y=4[/tex]
and not
[tex]2y = 4[/tex]
The suggestion to avoid such mistake is for the student to check the appropriate signs of each term before adding/subtracting.
