Question

(08.05)

Answer 1

The mistake is in step 3:

I: −2m =−12 − 2n
II: 2m = 8 + 8n

the student set both right sides of the equations equal (−12 − 2n = 8 + 8n), but the left sides aren't equal: first equation has -2m, second has +2m so the signs of one of the equations must be inverted first