Snap. Hum. La‑la. The 13‑year‑old computed a Pythagorean C scale from Middle C (261.63 Hz) to C' (523.26 Hz) using monochord ratios (1:2, 3:2, halving, two‑thirds), systematically doubling/halving octaves. Calculations show multiplicative reasoning, inverse proportionality, clear notation and units. ACARA v9 links: The Arts (Music) and Mathematics (Number & Measurement). Conclusion: exemplary mastery; recommend comparing equal temperament and hands‑on monochord/software verification. Plus ear training, reflective journal, presentation and portfolio inclusion.