(a) Prime cost method

Working: $30,000 × (1 / 5) = $30,000 × 0.20 = $6,000

First-year deduction: **$6,000**

(b) Diminishing value method

Working: $30,000 × (2 / 5) = $30,000 × 0.40 = $12,000

First-year deduction: **$12,000**

Controlling authority: **Division 40 of the Income Tax Assessment Act 1997 (Cth)**