How much salt does the waters of the Kuyalnitsky estuary (Odessa region) contain, if it is known that its area is 80 km2

How much salt does the waters of the Kuyalnitsky estuary (Odessa region) contain, if it is known that its area is 80 km2, the average depth is 3 m, and the average salinity is 12.5 ‰?

1) Find the volume of water in the estuary:
V = S × h = 80 km2 × 0.003 km = 0.24 km3
2) Let’s make the proportion:
1 km3 (1 ‰) – 1,000,000 tons of salts
1 km3 (12.5 ‰) – X t salts
X = 12.5 ‰ × 1,000,000 tons / 1 ‰ = 12,500,000 tons = 12.5 million tons
3) 12.5 million tons × 0.24 km3 = 3 million tons – salts are contained in the water of the estuary.
Answer: the water of the Kuyalnitsky estuary contains 3 million tons of salts.