Let the initial rate be r m/year. In the first 20 years, it retreated 20r meters. In the next 20 years, the rate was 2r, so it retreated 20 × 2r = 40r meters. Total retreat: 20r + 40r = 60r = 1,200 meters. Solving for r: r = 20. Retreat in second 20 years: 40 × 20 = 800 meters.

Tue, 05 May 2026 21:22:14 +0000

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