Show a maths result two different ways

Explain [MATH PROBLEM] for [LEARNER LEVEL] using a line-by-line symbolic solution and an independently described visual model. Name what each quantity represents, show units where relevant and finish by substituting the answer back into the original condition. Include one common wrong turn and why it fails. Do not skip a non-obvious algebra step or claim a diagram proves more than it does. Check that the visual and symbolic routes produce the same answer and that any rounding is stated.