Hi @chiabertrand, here is the grading for your brother's participation:

Corrections

• Advice him to observe all mathematical signs carefully the next time he is solving a math problem.
  N/b: When a positive value crosses over an equality sign it turns negative and when negative crosses equality sign it turns positive
• He should always solve first on a rough sheet before writing in his main book so as to avoid much cancellations and to enable his work look neat.

Thanks for your participation