I suggest for plan B: do 5-10 squats or sit-ups instead of eating tofu. Eat tofu just 3x weekly max.
Plan C:
Sing or do something inspiring for 10-15 min.
Check last Chiron's post on emotional centering and start practicing.
Your mind wanders to pleasant stuff. Your homework mihgt be unpleasant. Try to be inspired - what would it mean to the world if you mastered the skills they teach you now? What would mean for you to be increasingly smarter and capable? Incredible job, nice house, healthy food, vacations in the tropics .... etc?