Hidden goodwill is the difference between what C pays and his proportionate share of the firm's capital. Total capital before C = 20,000 + 40,000 = 60,000. C is entitled to 1/4 share, so expected capital = 60,000 × 1/3 = 20,000. But C pays 24,000, so hidden goodwill = 24,000 - 20,000 = 4,000. Since C gets 1/4 profit, goodwill is shared by old partners in their sacrificing ratio (equal), so hidden goodwill = 4,000 × 3 = 12,000. Alternatively, based on total capital after admission = 84,000, C's 1/4 share = 21,000, so hidden goodwill = 24,000 - 21,000 = 3,000, which gets adjusted among old partners.