Design one multi-step, real-world math problem appropriate for Grades 6–8 (challenging) that requires students to use proportional reasoning (ratios/scaling), to set up and solve a system of two linear equations for two unknowns, and to compute percent change; include the full problem statement with realistic numbers, all given data, and provide a complete, step-by-step solution with explanations, algebraic work, a final answer checked in context, and a brief note on common student errors and scaffolding strategies.